Читать книгу Naval Anti-Aircraft Guns and Gunnery - Norman Friedman - Страница 12
ОглавлениеA few navies, particularly the Royal Navy, became interested in anti-aircraft weapons even before 1914, just as naval aircraft were being developed.1 It was by far the most advanced in the world before and during the First World War. Wartime thinking and experience shaped inter-war British efforts, including the development of guns and fire-control systems in the 1920s, on which systems in service at the outbreak of the Second World War were based. British experience also helped shape the thinking of allied navies, probably particularly the US Navy (given its participation in the Grand Fleet) and the French and Italian navies. Moreover, British firms which developed fire-control devices based on that wartime experience (and on post-war British work) seem to have provided the basis for Japanese and probably for post-war Italian, Dutch and German fire-control systems.
It was soon obvious that few aircraft would be shot down by heavy guns. However, anti-aircraft fire could dissuade a pilot or force him to take evasive action which would ruin his aim, or at the least force him to fly so high that he could not hit a ship. It turned out that pilots were often almost completely unaware of bursts below or behind them. Shells should be set to burst ahead of the target aircraft, not least to ensure that the pilot realised he was under attack.
The other aspect of wartime naval anti-aircraft fire was the need to deal with scouting aircraft and Zeppelins. They had to be destroyed, or at the least driven off. During the First World War it seemed that shipboard fire could do that, but later it was clear that only fleet fighters could deal with scouts or snoopers.
The Royal Navy
Fire Control
In surface gunnery, which was difficult enough, range and deflection (leading the target in bearing) were not tightly bound together. It was possible to imagine tracking a target in bearing, finding the rate at which bearing changed, and providing enough deflection to allow for the time the shell would take to get there. In fact the bearing rate kept changing, but often not fast enough to complicate matters unduly. An aircraft seemed to move both horizontally and vertically, even if it was flying straight and level. A gunner always had to allow for two separate deflections. Instead of simply elevating for range, he had to add a tangent elevation (super-elevation in US parlance) to the vertical deflection, and the tangent elevation depended on the vertical deflection. The earliest anti-aircraft sights allowed for vertical deflection and tangent elevation; typically deflections allowed for the 20 seconds or so of flight of a 3in or 4in shell. It seems unlikely that anyone tried to add an allowance for a climbing or diving target, although everyone accepted that it was needed. The great development in sight design was to allow separate setting of vertical deflection and tangent elevation.
As in surface gunnery, it was unlikely that the first shell would hit, so much depended on spotting. Unfortunately there was no equivalent to the shell splash which showed that a shell fired at a surface target had missed (and, approximately, by how much and in what direction). Initially the British tried to solve the problem by adding tracer to their shells, but it turned out to be difficult for spotters to follow their flight (and also very difficult to tell whether a shell was near its target). Aircraft turned out to be so difficult to see under some conditions that the author of the Admiralty 1916 pamphlet on anti-aircraft fire considered that the control officer could not take his glasses off an air target, as he would be unable to reacquire it. Similarly, sight-setters could not move their eyes back and forth between air target and sight dials. By that time the British realised that the only practicable aid to spotting would be the burst of the shell. Fuses were set to burst at estimated target range.2
It turned out that observers at or near the gun could not be sure whether a burst was short or beyond the target. Was a shell bursting on its way up (i.e., at nearly the desired range) or on its way back down (i.e., fired at excessive range)? The control officer could only distinguish bursts as above, below, right or left. It was impossible to disentangle range (elevation) errors from errors in setting the length of fuse (fuse delay). A shell fired at too short a range might burst below a target. So might a shell fired at too great a range, whose fuse burst it after it passed over the target and dropped on the other side. Unfortunately British powder fuses functioned erratically – for example, the rate at which powder burned changed with altitude. Under some circumstances fuse problems might burst a shell as much as a thousand yards from the anticipated point. Thus development of a reliable mechanical time fuse became an important post-war project.3
Tests showed that neither shrapnel nor common shell (powder-filled) did sufficient damage. The Royal Navy therefore chose time- (and impact-) fused high-explosive (HE) shells, sometimes carrying tracers.4 Such HE shell did not become available until some time after mid-1917.
Surface guns had their range dials marked with curves so that gunners could instantly translate ranges into elevation angles. The natural extension was a fuse curve relating fuse action to gun elevation: not to range, but to what was visible: the sight angle at which the fuse would burst the shell. The shell would follow the trajectory given by tangent elevation plus vertical deflection, and at a timed point along that trajectory it would burst. Conversely, for any fuse setting a curve could be drawn showing the range and altitude at which the fuse would burst at various gun elevation angles. The object was to ensure that the shell would explode reliably at the desired sight angle, just as previously the object had been to ensure that the shell would arrive at the desired range along the chosen sight angle.
By 1917 the British were using elevation dials marked with fuse curves (range data were retained on the edge of the dial).5 By this time it was clear that the most difficult task for an experienced anti-aircraft officer was to choose the right fuse setting. It should be based on either target range or height and on the angle of sight to the target when the first round was intended to burst. No one could set fuses by eye, based on spots. Often what looked good from the gun was clearly wrong when viewed from a distance. An observer to one side could often see that not a single round burst within a thousand feet of the target. Typically the fuse setting was chosen based on a target speed-altitude curve drawn on a card.6 Since the process of fuse setting was relatively cumbersome, this choice had to come first, and it could not quickly be changed.
Once the fuse setting had been chosen, the elevation sight was set on the curve associated with it. As the angle of sight changed, a pointer automatically moved outward across the dial. When it met the fuse curve, it indicated the elevation which would cause a shell to burst on the line of sight. To keep the required fuse curves always under the pointer, the sight had to be readjusted constantly as the angle of sight changed. The complicated dial required its own highly-trained sight-setter in addition to the usual sight-setter. A simpler dial was therefore developed, to give as nearly as possible the same results with only a single sight setting for each fuse.7
To compensate for target motion, the British simply drew two more curves, one for an aircraft approaching at what seemed a reasonable average speed (in 1916, 80mph), and one for the same aircraft receding at the set average speed (the three curves were all marked on the dial, coloured black [static target], red [approaching] and green [receding]). For other speeds, small angular corrections sufficed. Once shells could reliably be fired to burst on the line of sight to the target, it seemed that gunnery could be reduced to lengthening or shortening the range. Spotting for line proved relatively simple, presumably because aircraft tended to fly directly towards the ship.
Cards and curves were needed because it became clear that few officers could calculate the change of range during the time the shell was in the air, let alone the dead time during which fuses and sights were being adjusted and also the loading interval at the gun (time between fuse setting and firing). A shell might take 20 seconds to go from gun to burst. During that time an aircraft might well fly 1200 yds (108kts). It seemed much simpler to concentrate on target height, which would not change much while the shell was in the air. For example, high-flying aircraft were unlikely to climb as much as 1000ft in a minute, and they proved unwilling to descend while under fire. Zeppelins did climb and descend more, but by 1917 they were apparently less important targets.
The combination between fuse timing, gun elevation and angle of sight was complicated enough to preclude, at least for the moment, any kind of dynamic fire control. A control officer could set fuses and aim a gun to create a burst at a predetermined place, but the set-up was too cumbersome to keep changing to deal with a moving aircraft. Multiple guns could create a zone of fire. By late in the First World War the British advocated creating multiple zones of fire through which the aircraft was expected to fly. This barrage was a burst of rapid fire (several rounds per gun), all on one line of sight, and all with the same fuse setting. In theory the barrage created a curtain of fire into which the aircraft would fly. Fuses would be set somewhat short for approaching aircraft. For slow targets, a variation of the ‘ladder’ technique used against ships was recommended. Burst or zone fire required that guns have ready-use ammunition at hand.8 In 1917 the Royal Navy introduced a fuse-setting instrument to guarantee that successive zones of fire would have a reasonable relationship to each other. It was based on the assumption that aircraft would fly level. The spotting officer had to estimate the speed of approach of the target (the instrument was set for 100kts, but could be adjusted).9 This zone approach had already been developed to deal with fast surface torpedo craft. No one considered it satisfactory. The main lesson of the dials and curves and zones was that calculation should be automatic and rapid.
By 1917 anti-aircraft organisation had been formalised. The control party consisted of a spotting officer; two men to work the fuse range indicator or card; a rangefinder operator; a rangefinder layer (pointer); a range scale reader; a communications party; and an observer to identify aircraft (typically with a high-powered telescope). Ships with two different high-angle (HA) guns (typically one 3in and one 4in) needed fuse calculators for each gun, preferably both using the same data. Each gun’s crew should include two sight-setters, one to keep the sights set to the chosen fuse setting, and one to apply vertical and horizontal deflection. Two more crew members were to set fuses and to raise ammunition from the ready-use boxes.
Perhaps the most important wartime lesson was that it was difficult to measure the range of a fast aircraft. Naturally the Royal Navy turned to its rangefinder maker, Barr & Stroud. That company sold coincidence rangefinders for surface and therefore now for air targets. Initially Barr & Stroud simply redesigned its rangefinder mounting so the instrument’s line of sight could be tipped up towards the aircraft. The French army was the first customer, with a 1911 request. Barr & Stroud delivered its first tippable MT mounting in 1913.10 The rangefinder itself was the standard portable army-type FT, which could have a base length of up to 2m. The Royal Navy bought some tippable rangefinders for trials, but disliked the technique.
For the Royal Navy, Barr & Stroud modified the 2m version of its FT rangefinder to swing into the vertical. It could measure both sight angle and slant range, and the combination gave target height. The rangefinder could swing back into the horizontal to give target bearing. In the latter half of 1914 the Admiralty ordered high-angle FT28 rangefinders (1m base) for ships armed with HA guns.11 Initially instruments read out only true (slant) range, but they were later modified to give horizontal range as well. Early in 1916 a 2m rangefinder was made, and after July 1916 trials, these instruments (FT29 on MT6 mounting) were supplied to capital ships and light cruisers towards the end of 1916 and early 1917.
Thus by late 1916, ships had 1m or 2m rangefinders with vertical bases, each with three operators: (i) trainer and operator; (ii) elevator; (iii) reader. In January 1917 it was proposed that a heightfinder be attached to the 2m rangefinder as a basis for sight-setting and fuse-setting. This new feature was embodied in the MT10 mounting, which was being supplied at the end of the war. MT10 presumably embodied a new feature Barr & Stroud offered in a new specialised anti-aircraft rangefinder supplied to the army (UB2, 1917). Using differential gearing, the instrument automatically converted target range and elevation into height. As with the FT series, there were three operators. Initial production went to the British army, which ordered 400 UB2s in November 1917.
Each measurement with a coincidence rangefinder took time; the faster the aircraft, the less accurate a series of ranges. It was impossible to use that series of ranges to deduce the speed of an aircraft. Post-war development was shaped by the realisation that although it might be difficult to measure range quickly enough, most aircraft flew straight and level. Rangefinders could measure height, using trigonometry. Although each rangefinder-derived height might be inaccurate, successive observations could be averaged. The exception was at low altitude, where even a large change in angle would not be associated with much change in height. At such altitudes ranges would have to be taken directly.
Guns
The Royal Navy first experimented with guns on HA mountings to defend fixed shore installations, particularly magazines. Experiments began at the end of 1912. At the end of 1913 the navy decided to go a step further and mount HA guns on board ships. It opted for a 3in 20 cwt semi-automatic QF gun on a roller-path mounting (the British Army 4in QF Mk IV proved unsuccessful). After successful trials, orders for 3in mountings were placed late in 1913 for the latest battleships, the Iron Duke and Queen Elizabeth classes (two 3in each). This weapon became the standard wartime Royal Navy HA gun. It combined a large enough shell with a high muzzle velocity (2600ft/sec) and a high rate of fire (twenty-two to fifteen rounds per minute); effective range was about 6500 yds. The gun was modified (in non-semi-automatic form) for destroyers and submarines with its sight and recuperator under the gun, and with a mounting which could better survive immersion in salt water. By November 1914 all battleships of the Grand Fleet had two HA guns of some type. About November 1914 some 3in HA guns were withdrawn from the fleet to supplement the anti-aircraft defence of London.
In May 1915 specially-designed HA mountings became generally available to the fleet, and they began to replace the locally-converted improvised mountings. The latter now armed auxiliary patrols. By the spring of 1916 all ships had their designated anti-aircraft weapons.
The standard late-war 4in Mk V gun (4in/45) equipped the inter-war Royal Navy. This one was photographed aboard Exeter when she visited the United States in the 1930s.
The 4in Mk V gun on its HA mounting, as shown in its 1918 handbook. The recuperator above the breech returned the gun to its firing position after it recoiled. Note the loading tray behind the breech, which was displaced to the left of the gun. The blank disk next to the gun is the fuse disc, used by the crew to associate a fuse setting with an elevation angle.
However, by that time it was increasingly understood that reconnaissance by Zeppelins had to be countered. It seemed that ships armed with more powerful anti-aircraft guns could provide what might now be called area defence and was then called offensive anti-aircraft warfare. Forty-four 4in guns (4in BL VII and 4in QF IV) were placed on modified 3in HA mountings (maximum elevation 60°) on board capital ships and light cruisers.12 Some battleships had one 4in in place of a 3in gun. At about the same time some destroyers were given ‘trap-door’ 4in mountings, the idea being to tilt the platform under the gun to increase its elevation. The idea proved unsuccessful and was abandoned.
As the Zeppelin problem worsened, a more powerful gun was developed: a 6in on an HA mounting. During 1916 some were mounted on board monitors and China gunboats on the British south-east coast, and others went into the land positions. This gun never proved satisfactory. It was difficult to load at high elevations and it was unwieldy. In effect the 6in experience showed that there was a practical upper limit to gun size – hence reach – unless radical changes such as power loading and power handling were made. Attention shifted back to smaller calibres.
At the end of 1916 work began on a new mounting for the 4in QF Mk V gun (HA III: 80° elevation). The first mountings were supplied in February 1918; it was the standard post-war capital ship HA weapon. Work on two other HA mountings began early in 1917: a 3in HA III for submarines and torpedo craft; and a 12pdr HA VIII (12pdr 12 cwt gun) for trawlers, minesweepers and other small craft. Meanwhile a broad policy for destroyers was adopted in mid-1916. The large new ones (‘V’ class and similar ships) were each to have one 3in HA II. The smaller modern destroyers (the ‘M’ to ‘R’ classes) were each to have one 2pdr pom-pom. Older ships would have one 6pdr on HA IV mounting or one 12pdr 8 cwt on a converted mounting or a Vickers 3pdr.
In 1918 the use of a larger calibre was being considered, its size limited by the weight of QF ammunition which could be handled without power. On this basis a 4.7in gun with an 80lb round (projectile and case) was chosen, and a few were ordered after the Armistice for tests. This gun armed the post-war Nelson class battleships. On the other hand, it could be argued that lighter guns such as the 3in and 4in had other roles. In 1918 there was considerable interest in dealing with suddenly surfacing submarines, and it was argued that 4in guns were not handy enough for that role. On that basis cruisers were armed with 3in rather than 4in HA guns. In 1919 most capital ships had two 3in HA guns, but the latest were scheduled to receive 4in instead.
Once war broke out, it was clear that much larger numbers of anti-aircraft guns were needed for lesser ships and craft. Existing mountings for Hotchkiss 3pdr and 6pdr guns were converted until a satisfactory new mounting could be supplied. These guns armed auxiliary patrol trawlers and similar ships. Maximum 3pdr Hotchkiss range was about 4000 yds, and maximum 6pdr range about 5000 yds. The higher-velocity Vickers 3pdr (which had replaced 12pdrs as an anti-torpedo boat gun about 1903) was considered a more effective anti-aircraft gun due to its high velocity and high rate of fire, though it was too light a gun; effective range was 5000 yds.
The existing Vickers 3pdr semi-automatic (i.e., single-shot) gun was mounted on a converted anti-aircraft mounting. A design for a special HA mounting was adopted shortly after war broke out (large numbers were supplied early in 1915). Maximum effective pom-pom range, as estimated in 1916, was about 4500 yds.
The next larger gun, the 12pdr (3in), was also adapted for anti-aircraft fire, and special HA mountings became available in 1915. At the time this gun was used largely by ships in the Nore, which it was hoped could shoot down Zeppelins en route to bomb London. As the preferred 3in 20 cwt gun became available in sufficient numbers, converted 12pdrs were shifted to auxiliary ships such as trawlers.
Vickers’ drawing of the version of the 4in HA gun it offered for export soon after the First World War, from its 1923 catalogue.
There was also interest in converting existing light machine cannon (pom-poms, both 1½pdr and 2pdr). A few 1½pdr pom-poms were mounted temporarily in ships of the Grand Fleet and in light cruisers at southern bases (Dover and Harwich); they were replaced by 2pdrs (delivery began in June 1915). The 2pdrs were issued on an urgent basis, without training personnel. It was therefore no surprise that they proved unreliable in early service. They were unreliable; it turned out that they had been made without using the necessary gauges and jigs, and so were not standardised. The pom-pom was recoil-operated, and guns had been assembled with too little recoil length. The cartridge cases also proved too weak. The gun seems not to have been entirely reliable until early 1918.
Issue to the fleet having been suspended for a time, it was resumed in November 1917. By this time the Germans had introduced remote-controlled explosive motor boats off the Belgian coast (the British called them distance-controlled boats [DCBs]). In a sense they were analogous to aircraft, and the obvious counter was the sort of automatic gun otherwise intended to deal with aircraft: the 2pdr pom-pom. Plans called for three guns in each capital ship, two in each light cruiser, two in each destroyer leader, and one in each destroyer. Supply was not yet complete at the Armistice. By the end of 1919, a total of 932 of these guns had been supplied.13
The pom-pom thus became and remained the key British automatic anti-aircraft weapon; between the wars it was mounted both singly and multiply. It was a cannon version of the first really successful machine gun, the recoil-operated Maxim, invented in 1884 by the American Hiram Maxim, and licensed to Vickers (it was standard in the British army by 1891). The name ‘pom-pom’ came from the sound of firing. In back of the bolt of the gun was a toggle joint, which could bend like an elbow when unlocked. Conversely, by straightening out it propelled the bolt forward and locked it onto the barrel. The Luger pistol used a similar toggle, whose joint formed the distinctive crosswise cylinder atop it. When the gun fired, barrel and bolt recoiled together. The toggle, which had been straight (to hold the bolt in place), was unlocked so that it could bend up to allow the bolt to move back from the barrel. As bolt and barrel moved back, the bolt was unlocked from the barrel. The barrel hit a stop and the bolt kept going back, the toggle bending and the spring compressing. By moving back, the bolt also tripped the ejector and also stripped the next round from the belt, which was above the barrel. The fresh round was pulled into a feed block directly behind the belt. As the spring moved the bolt back, the toggle pulled down the feed block into line with the barrel. Then the toggle straightened, pushing the bolt and the new round forward for another shot. This technique is called short recoil, because the length over which the barrel itself recoils is limited (typically ¾in for a Maxim rifle-calibre machine gun). Compared to the original Maxim, the Vickers gun (the pom-pom) differed in that the toggle opened above rather than below the barrel. The standard US Browning machine gun, which the US Navy used before and during the Second World War, also used a recoil-powered short-recoil action, but of a different type, without a toggle.
The standard First World War 3in anti-aircraft gun was Mk I (3in 20 cwt) on a HA Mk II mounting. It was tested in the autumn of 1911 as the future anti-aircraft gun for both army and navy (the navy considered its performance inadequate, but bought it anyway). In Mk II or IIA mountings it armed the following ships: all dreadnoughts except Audacious, all battlecruisers, Lord Nelson class, first five King Edward VIIs, Albion, Prince George, Courageous class, Furious, Vindictive, Minotaur class, Achilles, Cochrane, Duke of Edinburgh, Danae, Dauntless, Dragon, Carlisle, Ceres class, Caledon class, Centaur class, Cleopatra, Conquest, Arethusa class (except Galatea), Chester, Birkenhead and Birmingham, Chatham, Falmouth, and Bristol classes, all scouts (except Pathfinder), Diamond, all large monitors (except Raglan), Gorgon class, M16, M18, M20–M27, minelayers Amphitrite, Ariadne, Latona, carriers Hermes and Campania, balloon ship City of Oxford, and gunboats Cicala, Cockchafer, Cricket and Glowworm. Two guns appear to have been mounted on the submarine E4 in 1916 as an experimental Zeppelin trap. The Mk II gun (not semi-automatic) armed the flotilla leaders Bruce, Campbell, Douglas, Montrose, Scott, Stuart, Shakespeare, Spencer, Wallace, Kempenfelt, Lightfoot and Marksman, and all ‘V&W’ class destroyers, and the submarines J7, K1 to K17, K22 (ex K13), L1 to L4, L7, L15 and M1. In 1940 ‘A’ to ‘I’ class destroyers were ordered rearmed with a single 3in 20 cwt gun on a HA mounting in place of their after sets of torpedo tubes. The 4in gun was rejected because installation entailed too much work and thus too much delay, and magazine stowage presented great difficulties. An ideal position, in place of No 3 gun, was rejected because that gun was so much more effective than No 4 gun on deck. Not all of the planned rearmament was carried out. A few ships later received FKCs and the associated three-man rangefinders. This is the Mk II gun on the Mk III mounting. There was also a disappearing mounting.
A Vickers-built 3in 20 cwt gun, shorn of its sights, at the Finnish National Air Defence museum. (Dr Raymond Cheung)
During the war Italy was given a licence to produce pom-poms, which it designated the Vickers 40/39. Guns were sent to Russia. After the war Japan bought the pom-pom, which was the standard light Japanese light anti-aircraft gun until the mid-1930s, when it was replaced by the French Hotchkiss 25mm.
In 1914 the standard Royal Navy machine gun was the 0.303in Maxim, intended primarily for shore operations and to arm boats.14 These roles largely disappeared after the fall of Belgium, but the guns were now badly wanted for anti-aircraft use on board destroyers and small craft. Guns were surrendered by capital ships so that destroyers could have at least minimal high-angle armament. Until pom-poms became available in mid-1915, many destroyers relied on Maxims and on rifles for air defence. A few heavier Maxims (0.45in calibre) were given high-angle mountings and incendiary bullets.
A Vickers drawing of the 3in 20 cwt HA gun, as the company advertised it after the First World War. The disk with the curves on it is the fuse disk.
The leader Campbell shows her 3in gun amidships, as installed when she was completed. This gun replaced the after bank of torpedo tubes on ‘A’ to ‘I’ class destroyers as modified from 1940 onwards.
The Maxim was the army’s standard weapon, and it was soon evident that it had bought far too few. Thus in September 1914 many navy guns were given to the army in France, and others followed in early 1915 for the expeditionary force attacking the Dardanelles. Remaining guns in the fleet were redistributed so that each destroyer, torpedo boat or small unit operating off the Belgian coast could have a minimum anti-aircraft defence. Capital ships and the earlier light cruisers were left with two guns each. Later light cruisers, all destroyers and certain auxiliaries had one gun each. The War Office began to return Maxims as Vickers guns (in effect, improved light-weight Maxims) became available, but at the same time the Royal Navy was commissioning more and more ships which required machine guns (the official history specially mentions Q ships). Until early 1915 it was impossible to increase the number of Maxims per ship. The navy ordered Vickers guns, but all were diverted to the army because they were more suitable for work ashore; the army gave up all its Maxims in return.
A 12pdr on the HA/LA Mk IX mounting used during the Second World War. This gun was introduced as the main armament of the first British destroyers in 1893. Ammunition was semi-fixed rather than fixed. The standard First World War auxiliary weapon was Mk I or Mk II (the latter introduced for produceability but considered less reliable). Pre-war Mk I production was 1482, plus 1147 in wartime (511 from the United States), and transfers from the army. Mk II: 2010 guns; Mk III was 400 made in Japan. Production resumed for the Second World War, the gun being Mk V. Production amounted to 3494, including 1588 in Canada. Many or all of the Canadian guns were made by the Canadian Pacific Railway Ogden shops in Calgary, hence were called Ogden guns. Both Mks I/II and V were widely used during the Second World War, on board old destroyers, submarines, smaller warships (such as minesweepers, steam Bangor and some Bathurst class, and many large trawlers), auxiliaries and DEMS. The standard Second World War mounting was HA/LA Mk IX. Mk IX was HA Mk VIII modified for gunlayer training; in Mk VIII the gunner elevated the gun by wheel but trained it with his body. Note the characteristic shield; the larger 3in 20 cwt gun was unshielded. During the First World War HA 12pdrs armed the seaplane carriers Nairana and Pegasus and later ‘Hunt’ class minesweepers and boom-defence vessels. This Canadian-made Mk V is in the Alberta Military Museum. (Stephen Magusiak for the Military Museums, Calgary, Alberta)
Versatile shows the 12pdr 12 cwt gun (3in/40) which replaced her after bank of torpedo tubes as part of the emergency destroyer anti-aircraft upgrade program of 1940. In 1940 ‘V&W’ class destroyers were ordered rearmed with this gun (not the 3in 20 cwt) in place of their after torpedo tubes. Surviving old destroyer leaders kept their 3in 20 cwt gun.
Maxim production was suspended in 1917, this gun being superseded by the much lighter air-cooled Lewis gun, introduced into the Royal Navy in 1916. It had first been ordered by the army in 1914, and then used extensively on aircraft, including those of the Royal Naval Air Service. In 1917 Lewis guns were issued in numbers to submarines, minesweepers and patrol ships in the southern part of the North Sea, as they were being attacked at low altitude. They were also issued to defensively armed merchant ships working on the east coast, because they were subject to torpedo and strafing attacks by German seaplanes (there were two torpedo attacks in 1917). Late in 1917 Lewis guns were supplied to cruisers and destroyers off the east coast. By the autumn of 1918 all ships of the Grand Fleet had Lewis guns to deal with low-level attacks. These guns were also supplied to coastal motor boats, motor launches, submarines, and Q-ships. All had been equipped by early 1918. In July 1918 it was decided to arm the main fleet with Lewis guns to deal with the strafing threat to exposed personnel. The scale of supply was ten per capital ship, eight per cruiser or light cruiser, and four per destroyer. Special naval mountings appeared in the middle of 1918: twins for battleships and cruisers, singles for auxiliary craft. Coastal Motor Boats (CMBs) had both types. Due to shortages, many ships had the American-made Savage-Lewis, which was identical apart from some spare parts. At the end of the war the question of whether the future Royal Navy machine gun should be the Maxim or the Lewis had not been decided (the Lewis was adopted).
Many British First World War auxiliary patrol vessels were armed with Hotchkiss 6pdrs (2.244in or 57mm) in HA mountings.
This 47mm (1.85in)/50 superseded the 3pdr Hotchkiss as a standard light anti-torpedo weapon, and was first mounted in the King Edward VII class. With its higher velocity, it was a better anti-aircraft weapon than the Hotchkiss, and a HA mounting appeared in 1915. For a time these guns were on board the battleship Collingwood, the King Edward VII class pre-dreadnoughts, and many cruisers, monitors, and ‘G’, ‘H’ and ‘I’ class destroyers. (Ian Buxton)
In addition to the specialised anti-aircraft guns, the 1917 Admiralty pamphlet on high-angle firing, but not its 1916 predecessor, envisaged using low-angle guns against distant aircraft; this was later an important theme in British naval anti-aircraft thinking. At low angles it was preferable to work in range rather than in altitude, and range determined the fuse length. Unfortunately the target would be moving rapidly through successive fuse-range curves, so no one fuse setting would suffice for long. Barrage fire would be the only effective tactic. To this end, larger-calibre low-angle guns were being supplied with shrapnel shell using a No. 81 fuse like that supplied for high-angle guns. The use of surface weapons controlled for barrage fire became an important theme of later British anti-aircraft development.
A 2pdr (40mm) pom-pom is shown on board a drifter during the First World War, with a heavier QF gun (a 6pdr Hotchkiss) in the background. The water-cooled pom-pom, known as such because of the noise it made as it fired, was a revived Boer War gun on a HA mounting. It was a scaled-up equivalent of the 0.303in Maxim or Vickers-Maxim used in large numbers by the British Army. This weapon armed corvettes during the Second World War, and it was also mounted in the bows of ‘Hunt’ class destroyers to deal with E-boats (German MTBs). Pom-poms were also made in other sizes, such as 1¼pdrs and 1pdrs (37mm). The 40mm Bofors was apparently conceived to meet a Royal Swedish Navy requirement for a pom-pom replacement.
The 2pdr pom-pom is shown on its standard HA single mounting. During the First World War the 2pdr was made under license in Italy (as the 40mm/39), and between the wars it was sold in quantity to Japan. Many other navies adopted it; the main exception was probably the US Navy. Until it began to offer the quadruple 0.5in gun in the late 1930s, Vickers sold the 2pdr to all navies for which it built destroyers. Some of them retained it after the war. The 2pdr appears in many armament lists as a 40mm gun.
A 2pdr pom-pom on board HMCS Assiniboine during the Second World War. During the inter-war period the 2pdr replaced the 3in gun on board British destroyers, itself being superseded by the quadruple 0.5in gun. (RCN)
The Austro-Hungarian battleship Prinz Eugen shows a black-shrouded 7cm G. L/50 anti-aircraft gun atop her ‘B’ turret. She had two more atop ‘X’ turret. By the end of the war Prinz Eugen had two guns atop ‘B’ turret and one atop ‘A’ turret. Her sister-ship Szent Istvan had the gun atop ‘A’ turret, and the other two ships each had two guns atop ‘B’ turret. Actual calibre was 6.6cm. This Skoda gun was introduced in 1911 as an anti-torpedo (boat) weapon, and was modified in 1915 as an anti-aircraft gun on a new mounting. In 1918 the standard battery of a Tegetthoff class battleship like this one was sixteen 7cm/50, including three or four on anti-aircraft mounts. Other battleships also had these weapons.
Austria-Hungary
According to a post-war report prepared for the US Navy, the Austrians concluded during the war that anti-aircraft fire could deal only with an aircraft actually attacking a ship; for anything else fighters were needed.15 It was unlikely that fire would bring the aircraft down, so the object was to deter him from dropping bombs.16 The Austrians therefore adopted barrage fire, mounting groups of four guns on board large ships. Fire was controlled by an officer at one end of the battery, with a clear view of the sky. He had tripod-mounted Zeiss binoculars for target acquisition, marked so that he could indicate target bearing and elevation, plus a Zeiss stereo rangefinder to measure range and altitude (by elevation).17 He also had printed firing tables. Ready-use shells at the guns had mechanical fuses pre-set for various times. The commander estimated target speed, and he used a pocket watch to indicate direction, the XII being pointed towards the approaching aircraft, and VI towards the observer. The control officer had printed firing tables including graphs of trajectories with various elevations and fuse settings. The tables showed required gun elevation for a given target altitude, range, speed and course. Guns fired in barrage mode, each of the four guns being assigned a different elevation. Three salvoes were fired as quickly as possible, after which the battery was re-aimed based both on spotting and on any observed aircraft manoeuvres. The control officer communicated with the battery either by megaphone or by visual signals, but the order to fire or cease fire was given either electrically or by a whistle. On ships with only one or two anti-aircraft guns, the object was only to keep the aviator from dropping bombs with any accuracy. Torpedo boat divisions formed a single battery under the command of the chief boat. In moving ships, the stress was on firing as rapidly as possible, to force the pilot to fly higher. Ships in harbour consolidated their anti-aircraft batteries with those ashore, each being assigned a sector. By the end of the war this procedure was considered somewhat unsatisfactory.
It is not clear to what, if any, extent the Austrian system matched the German. The Austrians used Barr & Stroud coincidence rangefinders for surface fire, so it seems at least possible that the Germans convinced them to adopt stereo rangefinders for anti-aircraft fire.
The Austrians deployed a wide variety of anti-aircraft guns: 7cm (of 20, 26, 30, 45 and 50 calibre lengths), 7.5cm/30, and 9cm (lengths 35 and 45 calibres). At the end of the war they were about to deploy 10cm and 12cm anti-aircraft guns. Presumably the extent of anti-aircraft armament reflects the considerable threat posed by the Italian air force. The heaviest gun in service was the 9cm (3.5in)/45, which fired a 10.2kg shell with a muzzle velocity of 600m/sec (1968ft/sec). Surface range was about 7km (7650 yds). The gun carried a device to adjust elevation angle
France
Most wartime French anti-aircraft research was sponsored by the army, which was far more affected by air attack. The French defence organisation separated armaments (the role of the current Direction Générale de l’Armament) from the services, so the responsible Mission ballistique des tirs aeriens (MBTA) had representatives from army, navy, and armaments organisation headquartered at Gâvres. The French army introduced powder time fuses and the notion of fuse curves which showed fuse duration as a function not only of target range but also of target height (gun elevation). Pre-war methods of constructing firing tables, which had been proposed as early as 1888, were poorly adapted to high-angle fire against aircraft. Given the new technique, it was possible to construct meshes of curves showing trajectories at different elevation angles. Cross-curves at different ranges showed the altitudes shells would reach at different elevation angles. Duration markers were placed along each trajectory. For a gun firing at an elevation of 40°, for example, maximum range would be something beyond 10,000m. The shell would cross the 6000m range curve after flying for slightly less than 25 seconds, and at an altitude of slightly less than 3000m. The times in a printed version of a set of curves were 25, 30 and 35 seconds, and maximum elevation given was 80°. Thus to burst a shell at a range of 6000m and an altitude slightly less than 3000m, its fuse would have to be cut for slightly under 25 seconds. The gun would be elevated to 40°. The mesh of curves showed that a demand to burst a shell at a particular range and altitude corresponded to a particular elevation and fuse setting. The French saw such meshes as the basis for a future anti-aircraft fire-control system, and they published the relevant theory in 1919–21.
The standard French Navy anti-aircraft gun of the First World War was the 47mm (3pdr) quick-firing gun on a new anti-aircraft mounting. The gun had originally been adopted as an anti-torpedo (boat) weapon, and it was comparable to the contemporary Royal Navy 3pdr. This one is shown on board the battleship Courbet in 1918.
The same data could be used to construct an alternative set of curves in which the cross-curves were arcs of a circle drawn to indicate various ranges. The arcs were calibrated in elevation angle. On this polar graph were drawn curves for different ranges. Where these curves crossed the altitude curves indicated the elevation to which a gun had to be laid to reach a given range at a set altitude.
The French called the fuse curves an abaque (abacus). They could be turned into what the British fuse curve dial: a dial graduated for time of flight on its periphery. Curves for constant burst range were inscribed on the disk. The distance from the centre of the dial indicated altitude, the curves being functions of altitude and fuse duration (time). The indicator working with the dial was graduated in altitude. The dial was turned so that the pointer was on the curve for the desired burst range. Where it touched that fuse curve indicated the duration for which a fuse should be set.
In surface fire, the gun elevated to an angle set simply by target range, but in anti-aircraft fire the problem was complicated by the fact that the aircraft was already flying above the horizon. The French concluded that nothing short of the mesh of curves would make successful fire possible. They had to add superelevation to the future angle of sight of the target. Typically a pointer was raised or lowered as the gun was pointed up at the expected future angle of sight. The gun was then elevated so that the curve corresponding to expected range on the fuse dial met the pointer.
As elsewhere, wartime French attempts at anti-aircraft fire control were based on the assumption that the target would fly straight and level. The French adopted much the same technique as the British, concentrating on plan motion. They developed alternative electric and mechanical means of measuring the rate at which the angle of sight changed, which they called tachymetres.18 Both wind and aircraft speed were measured by time a cloud and the aircraft spent passing through a measured grill at an angle set for altitude. There was also a special sight to determine target course. These techniques, reflected in army M1917 equipment, were not of course well suited to a moving, rolling ship. However, their success encouraged post-war naval projects.
The French navy ended the First World War with these devices, mainly calibrated for the army’s 75mm gun. It knew that they were ill-suited to moving ships. Neither guns nor instruments were stabilised. The navy did plan to use 2m or 4m rangefinders and direct means of measuring angle of sight.
The standard wartime French anti-aircraft gun was an adapted 47mm M1902. Its trunnions were moved to its rear, so that the gun could elevate to nearly 90°. A reflector sight was developed by the naval gunnery directorate at Toulon. The pointer kept the reflected target image in coincidence with a cross in a collimator. The reflector sight permitted a gunner to look down rather than strain to look directly up at the target. This technique was effective as long as the target remained visible in the mirror, but target acquisition could be difficult, particularly in rough weather. The collimator was arranged so that the shell would be fired ahead of the target. Firing tables were devised for a target speed of 120km/hr (74.5mph), and fire was not opened until the target was within 2000m. At about the same time Le Prieur, who was responsible for important surface fire control devices, devised a very simple machine gun sight using what would later be called a cartwheel foresight, comprising concentric circles with radii every 20 to 25°. The pointer chose the radius which most closely approached the target, and the circle representing deflections for a set speed at a given range. This device survived in widespread post-war service, in France and abroad.19
The Japanese-built Arabe class destroyers transferred to France during the war had Japanese-built versions of the British Vickers 3in gun. As noted, submarines particularly needed anti-aircraft guns. French steam submarines were particularly slow divers. The wartime Dupuy de Lôme, Gorgonne and Nereide classes were all equipped with 75mm guns derived from the army’s weapons. They were on disappearing mounts which could elevate to 80° and depress to -10°.
Germany
Unlike the Royal Navy (and all other major navies), the Germans used stereo rather than coincidence rangefinders. It is not clear to what extent the Germans applied stereo ranging to anti-aircraft defence during the First World War. They do not seem to have developed any specialised anti-aircraft fire-control system. The principal wartime anti-aircraft gun was the 8.8cm/45, originally adopted to beat off surface torpedo attacks, and then placed in a new high-angle mounting. Battleships typically had two at the beginning of the war and four at the end.
Italy
The wartime Royal Italian Navy used 76mm/40 and 76mm/45 antiaircraft guns, the former of Schneider 1911, the latter of Ansaldo 1917 type. Many submarines had 3in/30 anti-aircraft guns. The Italians licence-produced the Vickers pom-pom as the 40mm/39.
Like the larger navies, the German navy continued to use its First World War medium anti-aircraft gun during the inter-war period, in its case the 8.8cm/45. Two shielded guns of this type are shown on board the cruiser Königsberg in about 1931. By this time work was beginning on an entirely new long-barrel 8.8cm gun, which in turn was soon superseded by a long-barrel 10.5cm weapon. Unlike the later guns, which were counterbalanced so that their trunnions could be very close to their breeches, the 8.8cm/45 was of conventional design.
The 8.8cm/45 gun on board the first German post-war cruisers was a shielded version of the World War I anti-aircraft mounting. (Drawing by Mirosław Skwiot, from his German Naval Guns: 1939-1945)
The armoured cruiser San Giorgio shows two of her 3in/40 anti-aircraft guns atop her after turret. They were 12pdr 12 cwt guns of British type; the Italians also used the 3in/45, presumably the Vickers 3in 20 cwt license-built by Schneider (it was designated a Schneider gun). (Lieutenant Commander Erminio Bagnasco)
The standard Japanese naval anti-aircraft gun introduced during the First World War was the 8cm (actually 7.62cm, or 3in). This one is at the Beijing military museum. Next to it is the twin version of the standard Japanese 25mm machine gun of the Second World War. (Dr Raymond Cheung)
Japan
Like the Germans, the Japanese adapted the gun they used to deal with surface torpedo attacks, in this case an 8cm (actually 3in, or 7.62cm). The mounting of the standard Type 41 gun was ordered adapted to high-angle fire (75°) in 1915, and it was officially adopted on 4 February 1916, mounted first in the Kongo class. This gun was redesignated 40 cal 8cm HA gun on 5 October 1917, and as the Type 3 8cm HA gun on 29 March 1921. Deliveries up to 1939 amounted to 530, and another 295 were delivered between 1940 and 1945. Successor guns are described in the chapter below on the Imperial Japanese Navy. The Japanese do not seem to have had any specialised anti-aircraft fire-control device during the First World War.
Russia
Design work on a 4in/35 AA gun was begun in January 1917 (it was also to be a submarine gun). No prototype was completed, and the Soviet Navy considered but rejected reviving the project in 1922–4 (it built the more powerful B-14 instead).
A 76mm/30.5 was designed in June 1914 and placed in production in 1915. None had been delivered by the outbreak of the Civil War, but the gun then entered service. It was the first specially-designed 76mm naval anti-aircraft gun, and production continued until early in 1934 under the Soviet designation 30-K. It was a light army weapon of 1903 revived for anti-aircraft fire on a balanced mounting designed in 1913. The gun was semi-automatic, with a vertical wedge breech and a single underslung recoil cylinder. Rate of fire was 10–12 rnds/min, the shell weighing 6.5kg (14.3lb); muzzle velocity was 588m/sec (1928ft/sec).
There was also a 63.3mm (2.5in) anti-aircraft gun, twenty of which were ordered on 25 November 1916 for the Black Sea Fleet; on 1 April 1917 they were ordered installed on board the battleships Sv. Evstafii, Ioann Zlatoust, Tri Sviatitela and Rostislav. This gun fired a 4kg shrapnel shell at a muzzle velocity of 686m/sec (2250ft/sec).
The standard wartime machine cannon was the 37mm Maxim. The Russians began production of the Vickers pom-pom, in effect a scaled-up Maxim (2pdr rather than 1pdr) during the war, deliveries beginning in May 1917. In addition, the Russians ordered the 37mm Maklin, a US air-cooled gun, in 1916 (sixteen delivered 1916, 200 in 1917).
The Putilov-made Lender 76mm entered Russian naval service during the Civil War. Production continued until 1934. It was a 1903 light army weapon revived for anti-aircraft fire on a balanced mounting designed in 1913 (the gun was balanced roughly at mid-length). This gun was semi-automatic with a vertical wedge breech and a single recoil cylinder underneath. This example is at the Finnish national air defence museum. (Dr Raymond Cheung)
Designs for HA mountings for standard naval guns (75mm, 47mm, 37mm) began about 1914, and there were also improvised (and never standardised) high-angle mountings for 102mm/60 and 63mm guns.
United States
Beginning in 1914, the Characteristics (staff requirements) of US warships included ‘aeroplane guns’. Just before the First World War the navy chose the 3in/50 as its preferred anti-aircraft gun for large ships. BuOrd adapted both the new 3in/50 Mk X and an existing 1pdr pompom for anti-aircraft use (the latter was analogous to the pom-pom used by the Royal Navy). Although some design calculations for Mk X were dated March 1913, work on a 3in anti-aircraft gun seems to have begun with a 3in/30 (tentatively designated Mk XI) in October 1914. In addition to the 3in/50, there was interest in a 3in/35 (Mk XI). The 3in/50 was soon chosen. The prototype Mk X guns were completed by the Naval Gun Factory in 1914–15, and guns and mounts were tested in January 1916. BuOrd estimated that the lethal cone for the 3in/50 shrapnel round extended for 120 yds (10° cone); for a high-explosive shell it would extend about 25ft. These figures defined the allowable error in anti-aircraft fire.
The 3in/50 was the first US Navy gun designed specifically for anti-aircraft fire. Two turret-top 3in/50 anti-aircraft guns are visible on board the battleship Wyoming during a 10 March 1926 sub-calibre main battery firing exercise off Panama. Turret-top positions gave the best fields of fire, but the guns could not be used during a fleet action (due to blast) and ammunition supply was difficult. The same arguments applied fifteen years later when light anti-aircraft guns were mounted on ships’ turret tops.
A standard 3in/50 in service in the Second World War. So many such guns survived from First World War building programmes that production of new ones was not necessary until 1941. Some versions (Mods) of this Mk 11 had a platform for loaders raised well above the mount base, but that was not the case here. Mk 20 was the new-construction Second World War mounting, distinguishable by a prominent counterweight above the gun. It was an interim version using existing barrels. Mk 22 was all-new construction. Mk 21 was the corresponding wet mount for submarines, with a different gun designed to survive immersion.
The battleship New York shows her turret-top and crane-top 3in/50s in a photograph taken in the 1920s. She and the other older battleships retained their 3in guns when the newer battleships were refitted with 5in/25s. Although a director for these guns was to have been devised after the Mk 19 was fielded for the 5in/25, that never happened before the war, due to the lack of money. Even after a simple fire-control system appeared in the form of the Mk 51 and director, it offered no blind capability, leaving ships entirely exposed at night.
The original version of the 3in/50 anti-aircraft mount, Mk 11, from the 1945 Gun Mount and Turret Catalog. (Photograph by Richard S Pekelney, Historic Naval Ships Association, courtesy of Mr Pekelney)
The first battleships to have anti-aircraft guns incorporated in their designs were the 1915 class (Mississippi class), with four 3in/50. In December 1914 the Navy Department approved installation of four 3in/50 each on board the new Nevada and Pennsylvania class battleships due for completion in 1916. Texas had the prototype installation (1916). In 1917, when requirements were being drawn up for new battleships, the US Navy’s General Board proposed replacing these weapons with a new 4in anti-aircraft gun. BuOrd protested that a 4in gun would be too massive, and that its trunnions would be too high for efficient loading. The battery of the projected battleships was set at four 3in/50s. The standard four-gun battery was doubled to eight during the first round of post-war refits (1919–21), at the cost of two open-mount 5in/51 anti-destroyer guns.
During the war many battleships were armed with two such guns atop an after superfiring turret, but by 1917 much heavier batteries were wanted. The battleships designed in wartime were given batteries of eight 3in/50, typically on the deck above the secondary battery.
Lesser warships were also given anti-aircraft batteries. Characteristics for an abortive scout cruiser showed two anti-aircraft guns, and those for the Omaha class showed two heavy guns and two machine guns; the ships were completed with four 3in/50 each. The first destroyer whose Characteristics included an anti-aircraft gun was the Caldwell class (Destroyer 1916), but the earlier Sampsons were completed with two 1pdr pom-poms and a pair of 0.30-calibre machine guns. The wartime flush-deckers were to have had the same battery, but given the scarcity of pom-poms they received instead one 3in/23 and two (sometimes three) machine guns. The 3in/23 was typically mounted forward of the bridge. It had been hurriedly developed to replace existing 6pdrs aboard 110ft sub-chasers, its principal merit for anti-aircraft service being that it could fit in the same space as the pom-pom. Although it survived into the Second World War on board ‘flush deck’ destroyers (including those transferred to the United Kingdom in 1940), the 3in/23 was considered grossly inadequate even in 1917. It never seems to have been given any special means of fire control for it. By the end of the war, BuOrd was working on an entirely new 1pdr intended as the basis for a more powerful anti-aircraft weapon. It never entered service.20
A Second World War 3in/50 (Mk 20 or Mk 22) in action aboard an escort, probably a destroyer escort. Note the counterweight above the sights. Note also the pipe rack to prevent the gun from firing into the ship, an indication that it was not director-controlled (a director would incorporate stops to prevent such firing).
The standard Second World War version of the 3in/50 anti-aircraft gun. The smaller drawing shows the Mk 20 version, which used existing barrels. The externally indistinguishable Mk 22 had new barrels. (Photograph by Richard S Pekelney, Historic Naval Ships Association, courtesy of Mr Pekelney)
The Second World War Mk 22 used new-production barrels. Mk 26 was a power-driven version intended to work with the new 3in/50 Mk 50 director. (Photograph by Richard S Pekelney, Historic Naval Ships Association, courtesy of Mr Pekelney)
The US Navy adopted the 3in/23 (Mount Mk 14) for destroyers during the First World War, apparently because more suitable automatic weapons were in short supply. Given its low velocity, it was obsolescent during the First World War, but it survived aboard ‘flush-deckers’ into the next war. The 3in/23 also armed sub-chasers, and for that reason some were transferred to Italy during the First World War (the Italians also received, and retained, US Colt machine guns). This Mod 1 elevated to 75°. It is shown on board a US destroyer in the 1920s. (USN via Joseph I Aguillard, Esq., USN Retired)
Mk 24 was an entirely new single mount designed by Northern Pump specifically for merchant ships. It was simplified by replacing the earlier hydraulic recuperator with a counter-recoil spring wound around the barrel, as shown here. Mk 24 in turn was the basis for the automatic 3in/50 produced as an anti-Kamikaze measure at the end of the war.
The 3in/23 Mk 14 mounting. (Photograph by Richard S Pekelney, Historic Naval Ships Association, courtesy of Mr Pekelney)
