Helicopter Sikorsky XHR2S-1 Serial 56-4X Register 133734 used by US Marine Corps USMC. Built 1955. Aircraft history and location Aircraft History 133734 US Marine Corps 1954-03-31Sikorsky S-56, cn 56-4X, ff:? del NPRO as XHR2S-1, 133734, 31Mar54 retained by Sikorsky for various tests, including twin tail rotors scr unk. Send Updates Use APP to upload photo @ (optional) When Now? / / Send