43, was an Imperial Japanese Navy Kaichū-Type submarine of the Kaichū III subclass.

For surface running, the submarines were powered by two 1,450-brake-horsepower (1,081 kW) Sulzer Mark II diesel engines, each driving one propeller shaft.

They were also armed with a single 76.2 mm (3.00 in) deck gun mounted aft of the conning tower.

43 was taking part in maneuvers off the harbor at Sasebo when she collided with the light cruiser Tatsuta.

43 sank 3 nautical miles (5.6 km; 3.5 mi) off Sasebo in 156 feet (48 m) of water.

[3] Using a telephone floated from the sunken submarine, a rescue party on the surface established contact with the crewmen trapped aboard her, who reported ever-deteriorating conditions[3] before falling silent about ten hours after she sank.

43 was partially raised and towed to Sasebo, where she arrived on 13 April 1924 so that salvage operations could be completed in the protected waters of the harbor.

[2] On 1 December 1927 she was reassigned directly to the Sasebo Naval District[2] and subsequently was used for trials.