525 SIKORSKY HNS-1 US COAST GUARD

The Sikorsky R-4 was a single-engine light multi-role steel helicopter of American production, in a classic arrangement with a main rotor and a tail rotor on the beam. The drive was provided by a single 200 HP Warner R-550 engine. The flight of the first prototype took place in 1942, and serial production continued in the period 1942-1944. The Sikorsky R-4 was the first mass-produced helicopter in the history of aviation and the first used in combat by the USAAF. The Sikorsky R-4 helicopter was built on the basis of the experimental VS-300 machine, also built by Sikorski. After passing street tests, also in field conditions, the machine was put into mass production. The main application of these machines was the rescue operations of allied airmen shot down on enemy territory. The machines were used primarily in the Far East, especially in Burma. Several prototype and serial versions of the R-4 helicopter were created. One of the most important was the YR-4B version, which had a reinforced fuselage and a main rotor. The machines were also used by Great Britain and Canada. Eventually, they were withdrawn from service by 1948.