The Cachalot-class submarines were a pair of medium-sized submarines of the United States Navy built under the tonnage limits of the London Naval Treaty of 1930. They were originally named V-8 and V-9, and so were known as "V-boats" even though they were unrelated to the other seven submarines (V-1 through V-7) constructed between World War I and World War II. An extensive study was conducted to determine the optimum submarine size under the treaty restrictions, factoring in total force, endurance, and percentage of the force that could be maintained on station far from a base, as in a Pacific war scenario. Joseph W. Paige
Design
Although externally much like the later "fleet submarines," internally the Cachalots were quite different. Due to pressure from the Submarine Officers Conference, During the war, the riveted boats would leak fuel oil. two-cycle direct drive main diesel engines, each, with one BuEng MAN two-cycle auxiliary diesel engine, The auxiliary engine was for charging batteries or for increased surface speed via a diesel-electric system providing power to the main electric motors.
Due to the full double hull design, the external tanks proved too narrow for easy maintenance, and the MAN diesels were a constant headache, demanding re-engining
Service
Despite the calculation process, size reduction had gone too far with the Cachalots, limiting their patrol endurance.