What was the Naval symbol S2 or S1 during WWll?

During World War II, the naval symbols S1 and S2 referred to specific types of submarines in the U.S. Navy. S1 indicated a class of submarines known as the S-class, which were small coastal submarines designed for operations in shallow waters. S2 typically referred to the S-class submarines that had been modified or upgraded. These designations helped in identifying and categorizing the various submarine models used during the war.