8th Year Type torpedo

The "8th Year Type" (十二年式) was a 61 cm-diameter torpedo of the Imperial Japanese Navy, launched from surface ships. It was later used as the template to develop the more advanced Type 90 torpedo. It was further derivatived in two variations, "Number 1" and "Number 2", having respectively a lighter and larger warheads.

History and development
The Imperial Japanese Navy (IJN) initially used 53.3 cm-diameter torpedoes like most other navies during this period, making the 8th Year Type the first-ever 61 cm-diameter torpedo put in service (exactly 609 mm). It was initially deployed for the Mutsuki-class destroyers and was also adopted for the newer Fubuki-class destroyers as well as several cruisers for their refits such as the Nagara-class cruiser, 61 cm-diameter torpedoes being the only standards for future ships until the end of World War II.

Hatsuharu-class destroyer and heavy cruiser remodels were also fitted with 61 cm-diameter torpedo launcher, but all ships equipped with those launchers were now using the newly developed Type 90 torpedo, which was also progressively replacing all 8th Year Type torpedoes in IJN service, now obsolete.

The torpedo used a four-cylinder Schwarzkopff radial engine, with a wet-heater using kerosene and compressed air. They were launched from the torpedo tubes, in either a three or four tubed-closed launcher configurations. This system was notably improved with the following Type 90 torpedo, replacing the propulsion and improving the launching mechanism.