Detailed history and photos of helicopter Sikorsky HO4S-3 Serial 55-721 Register 138598 used by US Navy USN Track service timeline and current status. Aircraft History 138598 US Navy 1954-05-26Sikorsky S-55 c/n 55-721, ff:? del USN as HO4S-3, 138598, 26May54. Send Updates Use APP to upload photo @ (optional) When Now? / / Send
