sentences:  Passive Underwater Fire Control Feasibility System
  
  Passive Underwater Fire Control Feasibility System (or Study) (PUFFS) was a passive sonar system for submarines.It was designated AN/BQG-4 and was primarily equipped on United States Navy conventional submarines built in the 1950s beginning with the , and also those converted to GUPPY III or otherwise modernized in the 1960s.