Developments thumb|A torpedo is loaded into a U-Boat through a torpedo hatch. Compared to their World War I equivalents, the German U-boat designs of World War II were greatly improved. By using a new steel alloy and by welding instead of riveting, they had stronger hulls and could dive deeper. The diving time was decreased to thirty seconds for a medium U-boat. The power of diesel engines was increased, so U-boats had a greater surface speed. Range was increased by installing fuel saddle tanks, which were on open to the sea on the bottom in order to balance pressure, with the diesel fuel floating freely on the seawater within the saddle tank. Also, a technique was developed for economical cruising where only one of the two diesel engines would be run and would drive the two propeller shafts through a coupling with the two electro engines.
Developments thumb|A torpedo is loaded into a U-Boat through a torpedo hatch. Compared to their World War I equivalents, the German U-boat designs of World War II were greatly improved. By using a new steel alloy and by welding instead of riveting, they had stronger hulls and could dive deeper. The diving time was decreased to thirty seconds for a medium U-boat. The power of diesel engines was increased, so U-boats had a greater surface speed. Range was increased by installing fuel saddle tanks, which were on open to the sea on the bottom in order to balance pressure, with the diesel fuel floating freely on the seawater within the saddle tank Also, a technique was developed for economical cruising where only one of the two diesel engines would be run and would drive the two propeller shafts through a coupling with the two electro engines.