It was in 1927 when I.J.N. received words from its agents working in England that the Royal Navy was experimenting with oxygen-fueled torpedoes. According to the report, there was a large oxygen generator at the torpedo test range in Weymouth, and the Nelson-class battleships were using torpedoes fueled with oxygen. The advantage of using pure oxygen for torpedo fuel was clear to everyone. In terms of weight, only 23% of the air is oxygen, and the rest is nitrogen and other elements which do not contribute to the combustion of the fuel and, therefore, are superfluous. But pure oxygen is prone to explosion, and was thought to be too dangerous to be used aboard a ship. If the mixture of fuel (kerosene or alcohol) and pure oxygen was ignited, it invariably caused instant explosion.

Japanese engineers tried many methods to burn oxygen and fuel safely in a torpedo, but they were unsuccessful. They told themselves that if the British were doing it, they could do it too. They were wrong, because the British had given up a long time before, deeming it too dangerous to use pure oxygen in a torpedo.

Japanese engineers first tried to use oxygen-enriched air (50%) in which they succeeded. Then they began to experiment with the method in which they first fed normal compressed air to the combustion chamber at the time of ignition, and then they gradually enriched the air with oxygen until, after some time, pure oxygen began to be fed. They finally succeeded in sustaining combustion with pure oxygen. In the new torpedo, cooling was obtained with sea-water instead of fresh water, contained in a tank in the traditional torpedo.

The performance of the new torpedo surpassed even the wildest imagination. It had an amazing speed and range. I.J.N. literally ran out of test ranges. The new torpedoes often hit houses on the beach and stopped in someone’s kitchen or bedroom. The torpedoes were found to be nearly wakeless, and it was often difficult to locate them after tests until light bulbs were places in their warheads.

The surface-launched Type-93 ‘LONG-LANCE’ 24 inch torpedo could travel 22,000 yards at a speed of 49 knots, or 44,000 yards at 36 knots. In contrast, the U.S. Mark 15 21 inch destroyer torpedo of 15,000 yards at 26.5 knots.

I.J.N. planned to engage the U.S. battle squadron with these formidable torpedoes before it reached the Western Pacific where the Japanese battle squadron would lie in wait to destroy it in a final big-gun duel. All the Japanese surface craft from the heavy cruiser down were crammed with torpedo tubes. For instance, the light cruisers OI and KITIKAMI had forty tubes each.

I.J.N. would also rely heavily on the submarine in the decimation of the U. S. battle squadron on its westward march. This was the reason why I.J.N. built large I-Boats with a very long range and a high surface speed. U. S. battleships were expected to travel at a speed of about 20 knots, and the Japanese submarine would have to be faster than that on the surface, in order to make repeated attacks on them. Such a high speed for a submarine would have been superfluous for the purpose of commerce raiding, but I.J.N. did not have commerce raiding on its mind when it planned its future submarine fleet. It had only American battleships on its mind.