03/31/2022. Remarks by Johan Visschedijk: "Further development of the Model VS-316A R-4/HSN/Hoverfly series was initiated by Vought-Sikorsky as the Model VS-316B before January 1, 1943. On that date the companies were separated and the 'rotor section' became Sikorsky Aircraft Division of United Aircraft Corporation.

Sikorsky continued the development under the new company designation Model S-49, using the same rotor and transmission system with an improved fuselage. Early 1943 the USAAF ordered a prototype of the Model S-49 as the XR-6 (serial 43-47955), powered by a 225 hp Lycoming O-435-7 engine, it first flew nine months later, October 15, 1943. It was followed by five XR-6A (s/n 43-28240 to 43-28244) with a 240 hp Franklin O-405-9 engine. Three XR-6As (s/n 43-28241 to 43-28243) were transferred to the USN for evaluation, redesignated XHOS-1, these received the BuNos. 46446 to 46448.

Under a Sikorsky license, Nash-Kelvinator of Detroit, Michigan, built 26 similar YR-6A (s/n 43-45316 to 43-45341, c/n 1 to 26) and a production run of 193 R-6A (s/n 43-45342 to 43-45534, c/n 27 to 219). Redesignated HOS-1, 36 R-6As were transferred to the USN under the BuNos. 75589 to 75624."