The PS-1 had not been in service long before the JMSDF requested the development of a search-and-rescue (SAR) variant. Shin Meiwa, being keen to pursue the aircraft's development, embarked upon fulfilling this request. By deleting much of the PS-1's military equipment, room was freed up to provide the aircraft with a greater fuel capacity, retractable landing gear, and rescue equipment. The new variant, which was designated the "US-1A", could also quickly be converted for troop-carrying. The US-1A was Japan's first amphibian, operating from land and sea, which meant that it could transfer survivors to land facilities via ambulance more quickly. First flown on October 15, 1974, it was accepted into service during the following year, and eventually 19 aircraft were purchased. From the seventh aircraft on, an uprated version of the original engine was used, all aircraft were eventually modified to this US-1A standard.