Five of the class received an additional pair of external bow torpedo tubes, probably early in World War II: "Porpoise", "Pike", "Tarpon", "Pickerel", and "Permit". The original Mark 21 3 inch (76 mm)/50 caliber deck gun proved to be too light in service. It lacked sufficient punch to finish off crippled or small targets quickly enough to suit the crews. It was replaced by the Mark 9 4 inch (102 mm)/50 caliber gun in 1943-44, in most cases removed from an S-boat being transferred to training duty.