TORPEDO DEVELOPMENT DURING THE GREAT WAR
The torpedo now entered a stage of maturity, and concomitantly left behind the great named individuals who had imagined it, conceived it, and brought it to this maturity. From here on the developments would be driven by conflict, and the engineers were simply cogs in the machine. The notable names in this new stage would be those of the users, not the makers. There is the name of just one last designer to retain: on the eve of the Great War Lieutenant F H Sandford invented the pattern-runner. Its introduction, however, would have to wait until the following world war. Also, just before the outbreak of war, the production of British torpedoes was again moved, this time to the Royal Naval Torpedo Factory (RNTF) at Greenock, Scotland.
During the war great use was made of the popular 18in and the newer 21in torpedoes – the latter introduced in 1910 – the smaller sizes being mostly obsolete, and used only for ships’ boats in cutting-out expeditions, such as the attempts to destroy the stranded submarine E 15 in the Dardanelles. However, early RN and German submarines did retain the latest 14in models and, of course, they were the first torpedoes used successfully in drops from aircraft. The German navy introduced an interim calibre, the 50cm, which was 19.7in diameter.
The Allied blockade of Germany resulted in major non-ferric metal shortages, leading to the German occupying troops scavenging lead, brass and copper from houses in Belgium and northern France. This led them to introduce short-term expedients such as the use of cast iron instead of copper for the piping runs of their U-boat diesel engines: confiscated submarines and diesel engines in Allied hands after the Great War would cause their new owners significant problems. Despite this, the Germans concentrated on producing high-quality torpedoes, probably by taking shortcuts elsewhere, as they believed that the submarine torpedo was the decisive weapon that would help them win the war. One side effect, of course, was that they would not be producing Schwartzkopff torpedoes with phosphor-bronze bodies. Bronze would, however, continue to be used to produce U-boat torpedo tubes.
For a similar reason, having designed a stable warhead explosive in hexanite, a mixture of TNT and hexanitrodiphenylamine, the Germans continued with its production to the end of the war. This contrasted with the attitude of the British, who in 1917 were forced to dilute TNT with ammonium nitrate to produce amatol, a slightly inferior quality explosive, due to TNT being required elsewhere.
The fear of the surface torpedo was probably greater than the actual physical damage inflicted on the battle fleets. A far more dangerous development was the sinking of thousands of merchant ships by German U-boats, the majority by the torpedo.
On the Royal Navy side there were many submarine torpedo successes, but doubly galling in view of the relative scarcity of German ship targets, far too many torpedo failures. These were tracked down to inefficient exploders. Fisher became enraged, and declared he would have Assistant Director of Torpedoes Charlton ‘blown from a gun’. The reasons were the same as would reappear in the US Navy nearly thirty years later: a failure to expend expensive torpedoes in live-firing exercises involving the use of warheads against hard targets, as opposed to the standard practice of substituting a practice head. The exploders sometimes failed to go off, and it took a considerable time to find and eradicate the problem.
Thus it was infuriating for the crew of the only ‘K’– class steam submarine which ever drew a bead on a U-boat, to actually hit it with an 18in torpedo, but have it fail to explode. This class thereby failed to kill a single enemy, although accounting for a good number of RN deaths through accidents.
Again, the small, fast and highly manoeuvrable ‘R’ class, the first true hunter-killer submarines, might have made more of an impact, and promoted the future use of this new breed of submarine, had exactly the same thing not happened to one of them, seeing their torpedo hit a U-boat without exploding.
The Germans, for their part, experimented with a very large torpedo of 600mm diameter (23.6in) which they intended as the future armament of their last super-dreadnoughts and cruisers, plus the very large prototype destroyers. Very few were produced, and there is no record of their combat use. There was a proposal for an even larger torpedo, the 70cm (27.6in) J9. They did, however, make considerable advances, introducing remote control of exploding motorboats by radio, and of aerial torpedoes by wire, and they even introduced a magnetic influence exploder, which again would come to maturity late in the following world war.
In 1917 the Germans designed an electric torpedo, capable of a speed of 28 knots over 2000yds. Despite its slow speed, it had several advantages over the thermal-engined types. It was wakeless, giving escort vessels no indication of the location of the U-boat which had fired it. It did not change its mass, as did thermal torpedoes as their air and fuel were used up, so trim remained the same throughout its run. Finally, in an economy geared for war production, the electric torpedo did not require the same amount of highly-skilled man-hours in its construction as did the thermal type: it could be built by less specialised firms. Fortunately, the Armistice intervened before any electric torpedoes were fired in anger by the U-boat fleet.
The Americans produced a small experimental electric torpedo only 71/4in in diameter and some 6ft long, and followed it by a full-size 18in weapon in 1919. Then they lost interest in electric torpedoes for over twenty years. When the USA entered the war in 1917, large numbers of flush-decker destroyers were ordered, and to equip them the firm of Bliss-Leavitt produced over three thousand of their 21in Mark 8 ‘steam’ torpedoes, a production record at the time. These would remain in service with the flush-deckers through to 1945, and many would cross the Atlantic to join the Royal Navy when fifty of these veteran destroyers were delivered to Britain in 1940.
BETWEEN THE WARS
In the early 1920s the USN decided to withdraw the underwater tubes from its battleships, followed by the removal of their above-water tubes, deemed too dangerous in a big-gun battle. Above-water torpedo tubes remained standard fittings on all new cruiser designs, but except for the Omaha-class ships – which could be used in the role of destroyer flotilla leaders as in the IJN – the tubes were removed from all US cruisers in the mid 1930s. This move was not the result of a desire to reduce top-weight, as all the early Treaty cruisers came in under weight, but on the grounds that their tactical deployment did not require them, cruisers being reserved for gunfire support of destroyer flotillas.
Meanwhile, major moves were made in terms of the propulsion units. By the end of the Great War the standard British torpedo engine was a wet-heater four-cylinder radial made of bronze, with integral cylinder barrels and heads as in contemporary automobile practice. Because of the increasing weight of the air flask, required to withstand ever higher pressures, experiments were made with hydrogen peroxide, which needed a lighter containment vessel, to produce oxygen via a catalyst. These developments were shelved by the British, but taken up by the Germans, the Japanese and the Americans in the latter part of the Second World War.
To obtain more power from existing pressure vessels, thought was given to using air enriched with oxygen – up to 57 per cent by weight, or even pure oxygen. The British 21in Mark VII of 1928 was the Royal Navy’s first enriched air torpedo, carried by the London-class heavy cruisers, and this led to the 24.5in Mark 1 installed in the Nelson and Rodney. Before the outbreak of the Second World War, however, due to corrosion problems with the air vessels, both enriched air models were changed to run on normal compressed air.
At around the same time, the British were perfecting the burner-cycle reciprocating engine, which retained the classic four-cylinder radial layout. The bore/stroke ratio of these compact radial units bore little resemblance to the contemporary automobile long-stroke inline reciprocating engine, with its inherent disadvantages of piston friction and heavy, out of balance, reciprocating weights. The radial engine could thus continue to rival the American preference for the turbine engine. The first British torpedo to use the burner-cycle engine was the long-lived Mark VIII for submarine use. It was a modernised model of the Mark VIII which would be fired against the General Belgrano fifty-five years later. The corresponding torpedo for surface ships was the Mark IX.
The Brotherhood burner-cycle engine was fed with compressed air at around 840psi. A small amount of paraffin was atomised in the air and burned. The resultant gas was fed into the cylinders at a temperature of 1000°C, and additional fuel was injected just before the piston reached top dead-centre. The compression caused the fuel mixture to detonate, driving the piston down as in a diesel engine. The exhaust gas was evacuated through ports in the cylinder, but there were also two auxiliary exhaust ports in the piston crown. By 1945 this impressive power unit would have been tuned to produce up to 465bhp, sufficient to propel a 21in torpedo at 50 knots. Plans to run a version of this engine on nitric acid promised to produce 750bhp, but the outbreak of war meant that it was never built.
In 1923 German experiments with electric torpedoes continued in secret in Sweden, and the design was finalised six years later. Since the Versailles treaty banned Germany from possessing submarines, the electric torpedo was held in readiness until Hitler came to power and began repudiating the terms of Versailles.
Magnetic influence exploders had been developed during the Great War, and the Duplex exploder was fitted to Royal Navy torpedoes from 1938. But the old problem of insufficient live-firing tests cropped up, and was to seriously affect their performances. The only navy to carry out large-scale live torpedo firing was the Imperial Japanese navy, which had expended many obsolete warships in tests in the lead-up to the Second World War. The Japanese saw in the torpedo the weapon they needed to give them an edge over the numerically superior US fleet in the Pacific. Japanese war strategy involved wearing down the US Navy in a series of actions across the Pacific Ocean until parity had been reached with the Japanese battle line, when the dreadnoughts would move in for the decisive final battle. A major part of this strategy depended on the torpedo: they set to work to produce the best in the world, and in this they succeeded.
Japanese development of an electric torpedo for submarines began in 1921, inspired by the model the Germans had introduced to their U-boats just prior to the Armistice. The design was finalised by 1925. The 21in torpedo was powered by two 54-cell lead-acid batteries feeding a 95ehp motor. It could run at 28 to 30 knots out to 7000m (7660yds), carrying a 300kg (660lbs) warhead. It became the Type 92 in 1934, but manufacture was suspended, ready for mass production in the event of war.
The Imperial Japanese navy studied other German late war developments, including the 600cm 23.6in torpedo. They had previously tried out the 27.5in Fiume torpedo produced in around 1900, and in 1905 they had ordered 24in torpedoes from Fiume for coastal defence. Now they decided to produce a heavyweight torpedo of their own for the anticipated conflict with the Americans. The result was the 24in Year 8 torpedo of 1919, capable of 38 knots over 10,000m (11,000yds) and carrying a 345kg (759lbs) warhead. Ten years later the 24in Type 90 appeared, capable of 46 knots over 7000m (7660yds) with an explosive charge of 375kg (825lbs).
They had briefly tested oxygen-enriched torpedoes in 1917. Future Admiral Oyagi, during the two years (1926–27) he spent at the Whitehead factory in England, heard rumours that the Royal Navy was fitting oxygen-fuelled 24.5in torpedoes in Rodney and Nelson. In fact the 24.5in Mark 1 originally ran on oxygen-enriched air, but on his return to Japan, Oyagi headed up a team to work on producing a version of the Japanese 24in torpedo to run on 100 per cent oxygen.
There were severe problems to overcome. The oxygen had to be prevented from coming into contact with any of the lubricants in the torpedo mechanism, to avoid the risk of explosion. More serious were the explosions which occurred in the engine combustion chambers as soon as the oxygen and kerosene fuel were injected. The design team overcame this hazard by starting the torpedo on compressed air, stored in a ‘first air bottle’ and only then gradually changing over to pure oxygen. They succeeded in producing a working torpedo, which was designated the Type 93, from the year 2593 in the Japanese calendar when the design was finalised.
The Type 93 oxygen-fuelled engine produced 520 horsepower at 1200rpm, compared with the 240hp of the British 24.5in and the 320hp of the initial Mark VIII. It could run at 49 knots for 20,000m (22,000yds), an exceptional performance. At 36 knots it would reach out to a phenomenal 40,000m (44,000yds). It carried a 490kg (1078lbs) warhead, capable of inflicting devastating damage. And it was practically wakeless. To profit fully from its deadly characteristics the IJN introduced power-reloading gear to their large fleet destroyers, following the provision of multiple reloads on board their cruisers.
Since the Japanese had previously had difficulty in forging the air vessels required for their licence-built Whiteheads, they constructed a special 4000-ton press to forge the body and after end of the flasks for the Type 93 out of steel billets. The air flask forward end cover was fixed with a large copper washer, the internal pressure keeping the joint gas-tight, and the arrangement proved extremely satisfactory.
The Type 93 was too large to be carried in submarines, so a smaller 21in oxygen torpedo was designed for them in 1935, the Type 95. It could run at 49 knots for 9000m (9840yds) and at 45 knots it reached out to 12,000m (13,000yds). The Type 95 carried a 405kg (891lbs) warhead. In 1943 the Model 2 would carry a warhead of 550kg (1210lbs). The Type 95 first air bottles often leaked, and while in the tubes on cruisers and destroyers it was a simple matter to verify the pressure of their oxygen-fuelled torpedoes at regular intervals and, if necessary, top it up, in a submarine this was not so easy, a factor leading to the electric Type 92 being resuscitated.
In 1937 the Japanese designed their third oxygen-fuelled torpedo, this time an even smaller 18in model, the Type 97, designed for midget submarines. It carried a 350kg (770lbs) charge at 45 knots over 5500m (6000yds). The original Type 97 would see action only once, during the attack on Pearl Harbor, as its leaky first air bottles were impossible to check and recharge, since the torpedoes were muzzle-loaded into the tubes before the start of a mission, and the crew had no access to the torpedoes when under way.
The Japanese pre-war torpedo arsenal was completed by the excellent Type 91 aircraft torpedo. They experimented with highspeed torpedoes for destroyers, the two built reaching 56 knots, and also with turbine torpedo engines, but neither development was pursued. Up until 1940 they used round-nosed torpedo heads, but in that year the Italian streamlined torpedo head was introduced and used on all types, with a claimed increase in speed of around 2 knots, with no increase in engine power.
The US Navy produced three new torpedo designs in the 1930s, which would continue to serve throughout the Second World War. The Mark 14 submarine torpedo was designed in 1931, and was a development of the previous Bliss-Leavitt designs. The destroyer version was the Mark 15, which was longer with a larger warhead, but otherwise differed in minor details only.
The US Navy had begun experiments with alternative fuels as early as 1915, and in 1929 had started a research programme at the Naval Research Laboratory. By 1934 they had produced ‘navol’, a concentrated solution of hydrogen peroxide in water to provide an oxygen source, burning alcohol as fuel. The projected Mark 17 Navol torpedo for destroyers was interrupted by the attack on Pearl Harbor and the urgent need to produce torpedoes of the existing types.