Examination of modern torpedo nose designs will reveal the extreme care used to ensure maximum laminar flow.
This was the codename given to a British version of the wartime German Ingolin torpedoes fuelled by hydrogen peroxide. Instead of building a new torpedo designed to incorporate the special requirements of this highly volatile fuel, British scientists attempted to modify the existing Mark 8 torpedo, substituting the HTP tank and catalyst system for the air flask, to produce the Mark 12.
This make-do-and-mend approach inevitably led to disaster. Following the sinking of HM Submarine Sidon, and a second Mark 12 explosion on the firing range, the project was cancelled. Other countries that took a more innovative approach to the problem succeeded in producing workable HTP torpedoes, and they entered service with the Swedish and Russian navies — although it is to be feared that the loss of Kursk may have resulted from the latest HTP incident. One example of Fancy is stored in the Aladdin’s cave that is Explosion in Gosport.
After the unfortunate Fancy affair, it is refreshing to describe a British success story. The Royal Navy began work in 1947 on a new homing torpedo based on captured German wartime examples. The electric battery-powered Bidder went into submarine and surface ship service as the Mark 20.
Harking back to the Brennan, and inspired by captured information on the German Spinne T10 torpedoes, the Royal Navy added a jettisonable wire spool to the tail of Bidder, and produced Grog, a wire-guided 21in submarine torpedo which went into service with the Royal Navy in 1966 as the Mark 23.
HEAVYWEIGHTS — NOVEL GUIDANCE AND PROPULSION SYSTEMS
Wire control was also used on the American Mark 45 torpedo, which first went into service in 1963, but for a different reason.
Profiting from German wartime designs, the Cold War-era Russian nuclear boats were displaying high speed, allied to deep diving abilities. They were, however, noisy boats and could be detected and tracked by their US Navy shadows, but sonar bearings alone were insufficiently accurate to ensure a kill with conventional torpedoes of the day. The Mark 45 was therefore armed with a W34 low-yield (11 kilotons) tactical nuclear warhead, designed to ensure destruction of the enemy boat by a proximity detonation. To ensure that full control was kept over the release of the nuclear weapon, wire control was added to carry out the detonation. Target guidance signals could also be sent via the wire connection, but ASTOR had no onboard homing ability.
The Mark 45 was 19in (483mm) in diameter, and was launched silently from a standard 21in tube by allowing it to swim out. It was 227in (5.8m) long and weighed 2400lbs (1100kg). Powered by a seawater battery and a 160ehp electric motor, it could reach 40 knots and had a maximum range of 15,000yds (13,650m), uncomfortably close for any vessel launching a nuclear weapon.
In 1976 the Mark 45 was replaced in service by the Mark 48, which is still the current USN submarine torpedo. The nuclear warheads were removed from the Mark 45s and a conventional warhead fitted by Westinghouse. These so-called ‘Freedom’ torpedoes were offered for foreign sale without much success.
The Royal Navy’s Mark 24 Tigerfish was a 21in heavy torpedo powered by chloride silver/zinc oxide batteries, for a top speed of 35 knots for final run in to target and a maximum range of 22 nautical miles (39,000m) at low speed. Wire-guided to the point of the launch submarine’s sonar target acquisition, it then used passive terminal sonar homing. A signal could be sent down the wire to make the Tigerfish switch between passive and active homing. It entered service in 1979.
Despite its ambitious capabilities, Tigerfish never lived up to expectations. Its guidance systems were hopelessly unreliable, and when HMS Conqueror was ordered to attack the General Belgrano in 1982, her commander opted to use the old traditional unguided Mark 8 torpedoes instead of his Tigerfish (see Part IV). Hampered by a lack of ultra-deep diving capability, Tigerfish was withdrawn in February 2004.
High-speed targets called for faster torpedoes, the rule of thumb requiring that the torpedo needs to possess a 50 per cent margin over the speed of the submarine it is attacking. Electric torpedoes were adequate for tracking down diesel-powered boats capable of 20 knots underwater, but nuclear boats running at 30 knots called for new propulsion systems.
An important innovation was the introduction of a new fuel for existing internal combustion torpedo engines, invented by Dr Otto Reitlinger, and accordingly called Otto fuel II. It has nothing in common with the ‘Otto cycle’ used to describe internal combustion engines, and is a powerful monopropellant. Otto fuel II is composed of the following synthetic chemicals (approximate percentages by weight): 76 per cent is a nitrated ester explosive propellant, propylene glycol dinitrate (PGDN); 1.5 per cent is a stabiliser, 2-nitrodiphenylamine; 22.5 per cent is a desensitiser, dibutyl sebacate.
A reddish-orange liquid, Otto fuel II is stable, not volatile, and needs no oxygen to initiate combustion: its three components will react among themselves when vaporised and heated. Its fuel energy density far surpasses that of the comparable-sized electric storage battery.
One of the major torpedoes to use Otto fuel II is the long-lived Mark 48. It entered service in 1972, replacing the Mark 14 and Mark 37 torpedoes in the USN submarine fleet. Designed to combat the fast and deep-diving Soviet Alpha class, the Mark 48 has been continually developed and upgraded to keep it in the front line. Its swashplate piston engine is powered by Otto fuel II and operates a pump-jet propulsor. The Mod 6 variant of the 1990s significantly reduced the noise level of the engine, making the Mark 48 more difficult to detect by its target. The destruction potential of the warhead, which is exploded by a proximity fuse, is augmented by the explosion of remaining fuel.
Performance details of the latest ADCAP (advanced capabilities) version are classified, but it is rumoured to have a maximum diving depth of 800m (2625ft) and a top speed of around 55 knots. The Mark 48 can be wire-guided, and has onboard active and passive common broadband advanced sonar system (CBASS). The most recent upgrade was intended to equip it for operation in littoral waters. The pump jet minimises vibrations emanating from the propeller wash undulations impacting the torpedo fins. The pump-jet propulsion is used in modern hunter-killer submarines for the very same reason.