V-3 was completed with two Busch-Sulzerdirect-drive 6-cylinder2-cycle main diesel engines of 2,250 hp (1,680 kW) each,[3][4] along with two Busch-Sulzer auxiliary diesel engines of 1,000 hp (750 kW) each, driving electrical generators. The latter were primarily for charging batteries, but to reach maximum surfaced speed, they could augment the mechanically coupled main-propulsion engines by driving the 1,200 hp (890 kW) electric motors in parallel via an electric transmission. Although it wasn't until about 1939 that its problems were solved, electric transmission in a pure diesel-electric arrangement became the propulsion system for the successful fleet submarines of World War II, the Tambor-class through the Tench-class. Prior to recommissioning in 1940, the auxiliary diesels were replaced with two BuEngMaschinenfabrik Augsburg Nürnberg AG (MAN-designed) 6-cylinder 4-cycle diesel engines of 1,000 hp (750 kW) each.[3][4] In 1942-43 Bonita was converted to a cargo submarine, with the main engines removed to provide cargo space, significantly reducing her speed on the remaining auxiliary diesels.[5]
Recommissioned on 5 September 1940, she departed New London, Connecticut on 17 November for Coco Solo, Panama Canal Zone. Bonita patrolled in the Pacific, off Panama, until she returned to Philadelphia for overhaul in October 1942. At this time she was converted to a cargo submarine with the removal of her main engines, severely restricting her speed on the auxiliary engines.[9]
Patrolling off the Maine coast until mid-1943, she then joined Submarine Squadron 1 (SubRon 1), SubDiv 13, on training duty out of New London. She remained on that duty until February 1945. Arriving at Philadelphia Navy Yard on 17 February, she was decommissioned 3 March and sold 28 October 1945.
^ abBauer, K. Jack; Roberts, Stephen S. (1991). Register of Ships of the U.S. Navy, 1775–1990: Major Combatants. Westport, Connecticut: Greenwood Press. p. 265. ISBN0-313-26202-0.