The launching procedure was as follows: a gear wheel moved by a rack on the aircraft on release opened a small air valve to start the gyros, then on water entry a flap opened a second larger valve admitting air to the engine; the horizontal stabilisers were locked in the ‘up’ position for the first 10m of the water run, after which they were freed off to move normally; to prevent damage on water entry, both propellers could freewheel until engine power was applied.
The IJN experimented with an oxygen-fuelled aircraft torpedo, the Type 94, with a 250bhp engine and a speed of 45 knots. It was discontinued when they realised that the main advantage of using oxygen, with all the attendant inconveniences, was extreme long range, and this was not required of an aircraft torpedo. They also built three prototypes of a large 23in diameter aircraft torpedo, the Type M, but dropped development when the new aircraft intended to carry it did not materialise in numbers.
Late in the war the IJN experimented with the Type QR, a standard Type 91 torpedo modified for attacks on submerged submarines. On water entry it was designed to circle and descend at the same time. The initial diameter of the spiral was about 300yds (290m), and the torpedo could continue this down to some 320ft (100m); fifty were made in 1945 and some issued to units but no record of their use has survived.
Another two anti-submarine spiral attack types were tested, the Model 6 and the Model 7, both unpowered, the first with a steel warhead and wooden body, the second with an all-steel lengthened body. Both had full-length wooden wings glued the full length of the body. Detonation was to be by proximity fuse. Testing was incomplete at the war’s end.
US NAVY MARK 13 TORPEDO
In common with the Japanese, the US Navy had retained full control over its air arm. The Mark 13 torpedo was to become a devastating weapon carried into action by the highly trained US Navy torpedo bomber pilots. But in the early days it acquired a bad reputation for erratic running or simply sinking without reason. One Grumman TBF pilot described it as apt to run ‘like a wild hippopotamus with its head above water’. After being far too often on the receiving end of the Japanese Type 91 which could be, and was, dropped fast and high, the US Navy settled down to devise solutions.
The modifications are shown in Part II, Chapter 14. A plywood drag ring was fixed around the warhead by a piece of wood wedged horizontally through the nose ring. It was an internally braced plywood tube, intended to increase air penetration and reduce the water entry shock by up to 40 per cent. The plywood structure broke away on water impact. It was this construction that Japanese Rear Admiral Naruse criticised, as the wood fragments risked being sucked into the propellers. A shroud ring around the tail helped prevent ‘hook’ or veering on water entry. In addition, a plywood rectangular box around the torpedo tail was held in place by wooden dowels, which sheared on water impact, shedding the plywood.
On leaving the plane, the starter mechanism began to run up the gyro and start the engine on compressed air only, to avoid the risk of the engine turbines overheating and burning out during the long air travel. A water delay valve prevented the fuel from reaching the engine. It was wired shut with copper wire on loading the torpedo underneath the aircraft. On impact with the water, the wire was broken and the main engine combustion cycle started. Similarly, the exploder was armed by a water impeller. To avoid the slipstream turning the impeller in the air, it too was wired shut with annealed soft copper wire, designed to shear on water impact.
By 1944/45 the optimum torpedo drop point was from 800ft at a speed of 260 knots, a huge improvement over the early war low and slow approach which was so dangerous for the aircrews. The US Navy made a training film in 1945, and the guidance it contained is described in Part IV.
PENTANE
Mark 21 Pentane was an experimental British air-dropped electric torpedo for anti-submarine work. The design was started 1947, after the collapse of the futuristic ‘Z — weapons’ programme, and by the mid 1950s had produced a working weapon system. Unfortunately, as a standard-sized 21in torpedo it had been designed for torpedo bombers, which had been phased out of service by the time it appeared. Helicopters of the era were not powerful enough to carry it, so Pentane was dropped in favour of the lightweight American Marks 43 and 44 antisubmarine torpedoes. One example survives in store at Explosion in Gosport.
For later developments, the lightweight homing torpedoes launched from fixed wing and rotary wing aircraft, and drones, as well as from surface ships, see Chapter 8.
CHAPTER 8
The Modern Torpedo Post-Second World War
Just as the aircraft carrier came to supplant the battleship as the decisive capital ship during the course of the Second World War, so in the latter half of the twentieth century the submarine came to threaten the place of the aircraft carrier in its turn. And the principal weapon associated with the submarine is, of course, the torpedo.
The post-war period was to see the struggle between submarines and surface ships (plus aircraft) continue at a frenetic pace, without ever the two elements having had the chance to put their tactics and technologies to the ultimate test. The two sinkings by submarine in 1971 and 1982 were classic encounters in the Second World War style, initiated by modern submarines against obsolescent opponents. The American and Russian nuclear undersea and above-water fleets may have played their dangerous cat-and-mouse game throughout the Cold War, but they never fired on each other — as far as they admit.
The 1940s and 1950s saw a great deal of development work, building on the experience of designs which had first seen action during the Second World War, and this work has continued into the present century.
BRITISH EXPERIMENTAL TORPEDOES
This was an experimental streamlined torpedo designed by Dr Barnes Wallis, inventor of the wartime ‘dam-buster’ bouncing bomb. The Heyday prototype was powered by a rocket motor fuelled by hydrogen peroxide and compressed air, constructed by a German scientist working at Vickers Armstrong. Laminar flow was a relatively new technique used during the war in the aircraft industry, and Wallis, one of its proponents, attempted to apply it to hydrodynamic research. With a standard torpedo shape of the 1950s, laminar flow could only be achieved around the curved nose section. The parallel body sides created turbulent flow. Barnes Wallis attempted to produce an experimental shape with a greatly increased area subject to laminar flow and therefore less skin friction, allowing a higher speed. The most he managed to achieve was laminar flow over just 28 per cent of the body, which in itself was a remarkable result.
Meanwhile, American studies revealed that laminar flow was extremely difficult to achieve and that the slightest blemish or fixture ruined the effect. In addition, the exaggerated egg-like profile of Heyday made it completely impossible to launch from a submarine’s torpedo tube and extremely difficult from the deck of a ship. Possibly it could have been used for air-launched torpedoes, but this was not pursued and the project lapsed. By good fortune Dr Wallis’s original test vehicle has survived, and is on display in the torpedo gallery at Explosion in Gosport.