Between 1971 and 1978, 21 PS-1 flying boats entered service with the JMSDF; starting in 1973, they were operated as Fleet Air Wing 31. The PS-1 ASW variant carried homing torpedoes, depth charges and 127mm Zuni rockets as offensive armament, but lacked any defensive weapons. It was equipped with dipping sonar, which had limited use as it required the aircraft to land on water to deploy. It could also carry 20 sonobuoys. It had a crew of ten: pilot, co-pilot, flight engineer, navigator and six sensor/weapons operators. On a typical ASW mission, a PS-1 would range over hundreds of square miles of ocean, landing between 12 and 16 times to dip its sonar.