Torpedoes

Torpedoes are essentially self-propelled mines. The weapon of choice for submarines, they were also extensively employed by surface ships, such as destroyers, and by aircraft. They were the only weapon that gave aircraft much chance of sinking a battleship. Because even the smallest ships could launch torpedoes capable of seriously damaging even the largest ships, torpedoes were the great equalizers of naval combat.

Japanese torpedoes were superb. The Japanese were employing 24” (610mm) torpedoes on their surface ships at the start of the war, versus 21” (533mm) torpedoes for most of the Western powers. Their best 24” torpedo, the Long Lance, had a half-ton warhead, used pure oxygen as its oxidizer, and had the incredible range of 30 miles (50 km) at 36 knots. It was also fairly reliable. This weapon proved deadly in night engagements throughout the war. The Japanese 21" submarine torpedo was also superb.

At the time war broke out in the Pacific, American torpedoes were very poor. The Mark 14 had a sophisticated magnetic detonator that was supposed to set the weapon off directly under the keel of a ship, where it would break the ship’s back. However, frugal budgets meant that it was live-tested exactly twice before being issued to the fleet, in 1926. One of the tests failed, which ought to have raised a red flag, but the Navy was reluctant to fund further live-firing tests. The weapon was standard for the more modern boats in the fleet by 1941. It took the Navy an astonishing two years to officially recognize that the weapon ran ten feet too deep, that the magnetic detonator was almost useless anywhere but the North Atlantic (and probably there as well), and that the contact detonator usually failed on normal impacts. In one notorious incident, a U.S. submarine commander crippled a large freighter with a spread of two torpedoes, then carefully squared off his boat and fired no less that thirteen additional torpedoes at a theoretically perfect angle of impact at the theoretically perfect range. Not one detonated. The problems with the Mark 14 were largely resolved by 1944, and U.S. submarines began to take a crippling toll of Japanese warships and merchantmen; but the Mark 14 never became a great torpedo.

One reason why the magnetic detonators were retained for so long was that the Mark 14 had a small warhead, just 500 pounds (228 kg) of explosive, which was less than half the weight of the Long Lance warhead. This was inadequate against the underwater protection of capital ships, and could not even guarantee the sinking of a large merchantman. The torpedo had to explode under the keel of the target to ensure destruction.

American aerial torpedoes were also poor at first, requiring a very low-speed, low-altitude drop that was nearly suicidal for the attacking aircraft. Later torpedo models were much better, being equipped with a nose drag ring to reduce the rate of fall and allow the torpedo to be dropped from higher altitude and at a higher speed. The Mark 24 "Fido" homing torpedo was deadly effective against German submarines, but saw little or no use in the Pacific. However, a submarine version, the Mark 27, was used only in the Pacific. This torpedo was slow and carried a very small charge, but it was very effective in its intended role as an anti-escort torpedo. The torpedo would home in on and destroy the screws of an escort vessel, rendering it hors de combat if it was not sunk outright.

The American Mark 15 destroyer torpedo suffered from the same deficiencies as the Mark 14 submarine torpedo.

Not only did the Americans suffer from poor torpedo quality early in the war; their torpedo production facilities were inadequate to wartime demand. Some 300 torpedoes were lost when the Japanese bombed Cavite, which was a substantial fraction of the Navy's entire reserve. American submarines occasionally went to sea armed with mines instead of torpedoes, and were instructed to fire only one or two torpedoes against merchant targets. Fortunately, production ramped up later in the war, ending the shortage.

British torpedoes were intermediate in quality. They had reliable contact detonators by 1941, but nothing like the range of the Long Lance.

Morison quotes the engineering officer of Hornet on the effects of a torpedo hit:

A sickly green flash momentarily lighted the scullery compartment and seemed to run both forward towards Repair Station 5 and aft into the scullery compartment for a distance of about 50 feet. This was preceded by a thud so deceptive as to almost make one believe that the torpedo had struck the port side. Immediately following the flush a hissing sound as of escaping air was heard followed by a dull rumbling noise. The deck on the port side seemed to crack open and a geyser of fuel oil which quickly reached a depth of two feet swept all personnel at Repair 5 off their feet and flung them headlong down the sloping decks of the compartment to the starboard side. Floundering around in the fuel oil, all somehow regained their feet and a hand chain was formed to the two-way ladder and escape scuttle leading from the third deck to the second deck....

References

Blair (1975)

Campbell (1985)

Morison (1949, 1951)

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Torpedoes

Japanese torpedoes

U.S. torpedoes

British torpedoes