Submarines became the United States most effective weapon against the Japanese after the fall of Hawaii. The Japanese had no means of detecting American subs. Thus, the Americans could sink Japanese cargo ships or shell the islands with relative impunity.
The Submarine also proved to be an extreme danger to Japanese aircraft carriers, as submarines badly damaged the Soryu and the Zuikaku. By 1943, U.S. submarines had played a critical role in cutting the supply lines between Japan and Hawaii, thus substantially aiding the U.S. invasion that year.
Tiny submarines, disguised as dolphins to fool spy satellites, ferried members of the Second Irgun to and from the coast of Palestine. Irgun member Yakov thought this poetic as it reminded him of the story of Jonah being swallowed by a large fish.
Submarines or submersibles were used by the C.S. Navy and other navies during the Great War to raid enemy shipping and disrupt supplies faring considerably better than the Confederate surface fleet against the larger and more powerful U.S. Navy.
Submarines were crucial to Earth'swar effort against the Race's Conquest Fleet because the Race, hailing from a desert planet, had no concept of them. The Race lacked the means to destroy them underwater, which meant that submarines could be used to transport crucial supplies and personnel between the resisting humanpowers with minimal danger. Submarines were used to transport plutonium seized from the Race to the United States and foreign ministers to London for the Big Five conferences. American and German submarines carrying atomic bombs destroyed the Race-occupied cities of Miami, Rome, and Alexandria by sailing into the ports undetected and detonating the bomb aboard the ship.