I-121-class submarine

The I-121 class submarine (伊百二十一型潜水艦,) was a class of submarine in the Imperial Japanese Navy (IJN), serving from the 1920s to the Second World War. The IJN classed it as a Kiraisen (機雷潜).

Construction
The Empire of Japan received six U-boats as a reparation payment after World War I. The IJN copied SMU U-125 and designed the I-21 class (later renamed I-121 class) minelaying submarine. Six boats were ordered, of which four were completed, two were cancelled. All boats were built in the Kawasaki Yard at Kobe.

Service
When World War II began, they were considered obsolete and used as minelayers and supply submarines for flying boats in the Pacific. Three boats of the class were lost in action. The I-121 survived the war and was sunk as a target post war.