Long Lance:
At the outbreak of the war, the Japanese Navy possessed some of the world’s finest torpedoes, including the fabled Long Lance. The quality of these weapons was no accident, but rather the result of Japan’s intensive efforts during the 1920’s and 30’s to make good the shortcomings of her battle fleet. Laboring as she did under the unfavorable 5:5:3 ratio of capital ships imposed by the Washington Naval Treaty, Japan would most likely be at a disadvantage in any Pacific conflict with the United States. She also knew well enough that the U.S. modeled its fighting doctrine on the famous ‘Plan Orange’, which called for an advance of the American battle fleet across the Pacific to relieve the Phillipines. It was anticipated that at some location in the Western Pacific a decisive battle would be fought. In Japan’s view, some means must be found to offset its disadvantage in capital ships before this battle occurred, or its inferior batle line would be destroyed by the American force. Torpedo tactics and night combat were seized upon as one way to whittle down the American battle line as it made its way across the Pacific. Accordingly, Japan worked diligently to develop the tactics needed to implement this new doctrine, and also to create the weapons with which to carry it out. The result was that Japanese torpedoes showed a steady progression of improvements throughout the 1930’s, culminating in the devlopment of the famous ‘Long Lance’ in 1935.
Designing and perfecting the Long Lance required solving some extremely difficult technical problems, most of which centered around the usage of pure oxygen as a fuel (rather than compressed air). Compressed air is nearly 77% nitrogen, which is useless for combustion, and also contributes to the visibility of the torpedo by leaving a bubble track on the surface. The usage of pure oxygen promised far greater power and propulsive efficiency, but it came with certain costs. The most glaring of these was how to use pure oxygen safely aboard a ship or submarine, given its inherently inflammable nature. Premature detonation of the torpedo upon firing was also a problem. However, the Japanese overcame these hurdles. Further, through meticulous live-testing of their weapons against ship targets, they perfected a warhead detonator that was rugged and reliable (The U.S. Navy’s BuOrd could certainly have taken a lesson or two here). The resulting weapon, the Type 93 torpedo, was fantastically advanced in comparison with its Western counterparts, possessing an unequaled combination of speed, range, and hitting power. This weapon, coupled with the flexible battle tactics practiced by Japan’s cruisers and destroyers, led to victory after victory in the early stages of the war. Only as American radar and gunfire control became increasingly sophisticated would the Japanese advantage in night battles begin to disappear, and even then a Long Lance-armed Japanese destroyer was still a thing to be feared.
http://en.wikipedia.org/wiki/Long_Lance
and this:
At that time, US Naval Intelligence was unaware of the advances the Japanese had made in torpedo technology. One of these advances was the Japanese 24 inch diameter “Long Lance” torpedo, which carried a charge equivalent to 891 pounds of TNT. A Long Lance torpedo essentially defeated the USS North Carolina’s side protective system. The ship was hit by chance at its narrowest, and therefore most vulnerable part of the side protection system. An Iowa Class battleship would have taken lighter damage from the torpedo due to an improved torpedo protection system over the North Carolina Class.
A torpedo is a self-propelled projectile carrying a warhead which detonates against a ship’s side below the waterline. It was the most destructive naval weapon of the Second World War and the best of these was the Japanese Long-Lance.
In 1941 the Japanese Navy was the third largest navy in the world, after the US Navy and the Royal Navy. It had 100 destroyers, 18 heavy cruisers and 18 light cruisers. Most destroyers and cruisers were fitted with the 24-inch Long Lance torpedo. This oxygen-powered weapon could deliver a 1,000lb warhead at 49 knots over almost 11 miles.
finally:
The Type 93 had a maximum range of 40,000 meters with a 1,080 lb (490 kg) warhead. In comparison the 16 inch /L45 guns mounted on the then-current US Colorado-class battleships fired a 2,110 lb (957 kg) shell to an absolute maximum range of 39,600 yards (36,210 m). Practical ranges for both weapons were much shorter, but still fairly comparable overall. Too large to fit in the standard 21-inch torpedo tubes, it was usually launched from the decks of surface ships, but some submarines also had deck-mounted launchers.
The Japanese Navy outfitted many of its destroyers and cruisers with the Type 93 torpedo. The long range, speed, and heavy warhead of the Type 93 gave these warships a formidable punch. Most also carried reloads, something that other navies did not like to do. The US Navy in particular completely did away with torpedoes for its cruiser force, preferring instead to mount massed batteries of radar-aimed quick-firing 6 inch or 8 inch (152 or 203 mm) guns.
In early battles, Japanese destroyers and cruisers were able to launch their torpedoes from over 20,000 metres out at unsuspecting Allied ships that were attempting to close to gun range, expecting torpedoes to be fired at less than 10,000 metres, the typical range of that era. The losses sustained in such engagements led to a belief among the Allies that the torpedoes were being fired from submarines operating in concert with the surface ships but at much closer ranges. On rare occasions, the very long range of the torpedo caused it to strike a ship that was far behind the intended target. The Type 93’s capabilities were not recognized by the Allies until one was captured intact in 1943.
conclusion: 1)Jap destroyers may get preemtive attacks because of the long range of this weapon or 2) or planes will get that +1 combat modifier for naval strikes ( fighters only).