The Imperial Japanese Navy operated the most varied fleet of submarines of any navy, including "Kaiten" crewed torpedoes, midget submarines ( and es), medium-range submarines, purpose-built supply submarines and long-range fleet submarines. They also had submarines with the highest submerged speeds during World War II (s) and submarines that could carry multiple aircraft (s). They were also equipped with one of the most advanced torpedoes of the conflict, the oxygen-propelled Type 95. Nevertheless, despite their technical prowess, Japan chose to use its submarines for fleet warfare, and consequently were relatively unsuccessful, as warships were fast, maneuverable and well-defended compared to merchant ships.