The submarines were medium-sized submarines of the Imperial Japanese Navy (IJN), serving during the 1920s and World War II. The Type L submarines were built with Vickers naval technical guidance. All boats were built in the Mitsubishi Heavy Industries-Kobe Shipyard by the contract with Vickers.
The Type L submarines were divided into four classes:
In 1916, the Mitsubishi Shipbuilding Corporation got the Vickers L class submarine informations. Mitsubishi which lost competition to the Kawasaki's Type F submarines (Fiat-Laurenti design, Ro-1 class and Ro-3 class), bought the license for the L class submarine from Vickers. The IJN hoped an improvement of submarine technologies will be achieved and ordered this submarine from Mitsubishi. Mitsubishi bought six submarine kits, and built two boats by semi-knock down. The submarine crews were satisfied with the Vickers diesels because they proved to be reliable. The IJN studied the diesel engines and made many variants of similar design, for example: Kampon Mk.24 diesel for the Ro-100 class.
The Type L2 had minor changes from the Type L1. The changes were:
The Type L3 is a license production model of the British L class submarine Group 2.
The Type L4 is a license production model of the British L class submarine Group 3. Their performance was good. The IJN was satisfied with them and stopped the development of Kaichà « type submarines for a long time. Later the IJN was not able to regain the technical delay in development of the medium-sized submarines until the end of the Pacific War.