Helicopter Sikorsky HRS-1 Serial 55-021 Register N4780S 127787 used by US Marine Corps USMC. Built 1951. Aircraft history and location Aircraft History 127787 US Marine Corps 1951-04-26Sikorsky S-55 c/n 55-021, ff:? del USMC as HRS-1, 127787, 26Apr51 N4780S - ex 127787 Send Updates Use APP to upload photo @ (optional) When Now? / / Send