I-121 
- TYPE: Submarine
- DISPLACEMENT SURFACED: 1,383 t (1,405 tnes)
- DISPLACEMENT SUBMERGED: 1,768 t (1,796 tnes)
- MACHINERY: Two Screws, Diesel/Electric Motors;
2,400/1,100 hp - LENGTH: 269 ft (82 m)
- BEAM: 24.7 ft (7.52 m)
- DRAUGHT: 14.5 ft (4.42 m)
- PERFORMANCE SURFACED: 14.5 knots
- PERFORMANCE SUBMERGED: 7 knots
- ARMAMENT: 4 533mm TT; 1 140mm guns;
2 mines - SURFACE RANGE: 10,500 nm (19,456 km)
- CREW: 75
- LAUNCHED: Unknown