Hello everyone,, At the beginning of WW2, the biggest initial change in comparison to the First World War was the newly available radio technology, along with the new tactics this enabled – mainly the Rudeltaktik, or wolfpack tactic, whose foundational concept was to attack a large convoy with an equally concentrated "pack" of U-boats. Movement was centrally controlled by the Befehlshaber der U-Boote, BdU, or Commander of Submarines, while submarines patrolled likely convoy routes individually. Once an enemy convoy was located, the spotting submarine alerted the BdU, who relocated several submarines from around the area to the scene of the convoy. Once a sufficient number of U-boats (compared to the expected threat of the convoy) gathered, the BdU gave clearance for an attack. While the Rudeltaktik proved to be a serious threat to Allied ships, it also had some blatant weaknesses – namely the heavy reliance on radio communication to organize the attacks, which was effectively met with countermeasures: High-frequency direction finding, abbrev. HF/DF and commonly referred to as huff-duff, allowed Allied naval forces to determine the location of the transmitting U-boats and attack them. Furthermore, air cover offered by blimps, planes with radar and escort carriers allowed submarines to be spotted as mobdro.bio/ luckypatcher.tips/ kodi.bio/ they waited to attack convoys. The US later adopted the wolfpack tactic, although without central coordination. Submarines proved to be effective weapons on all naval theaters. Both US Navy and Kriegsmarine mainly deployed submarines in economic warfare, to disrupt enemy logistic. After the US entered the war, German U-boat leadership changed the focus from blocking the UK to a strategy to sink more hold than the enemy could produce (Tonnagekrieg). This made deployment sites secondary, and German U-boats were fighting in all seas, only restricted through technical and supply limits. Due to allied technological advancement, like radar, HF/DF and the deciphering of the Enigma-decyphering, and material superiority with simultaneous overextension of Axis' resources, the German U-boat war was historically lost by May 1943. There was still some technological advancement, which came too late to influence the war, but still led to strategic changes in warfare. When it comes to the Pacific theatre, Japanese submarines didn't play a large role. They were varied, but not modern, as they had an emphasis on surface vessels. Their main deployment was against battleships, their sinking rates thus very low. The US Navy, applying the wolfpack tactic, was far more successful and sunk major battleships and disrupted Japanese merchant shipping. The latter significantly contributed to the Allied victory in the Pacific, by cutting off Japanese supplies and resources, 2% of US-American marine personnel were responsible for destroying 55% of Imperial Japan's total tonnage. However, the casualty rate for submariners is the highest of all US military service branches with 22%. So all in all, the biggest differences between the First and Second World War were given thanks to technological advancement. The main doctrine was economic warfare, which remained consistent until the late phase of Atlantic U-boat warfare, and unchanged for the Pacific theatre. Sources: Paul G. Halpern: A Naval History Of World War I, 1995 Clay Blair: Hitler's U-Boat War: The Hunters, 1939–1942, 1996 Clay Blair: Hitler's U-Boat War: The Hunted, 1942–1945, 1998 Clay Blair: Silent Victory. The U.S. Submarine War Against Japan, 1975.