This is a Notable Record milestone.
The exact month and day are unknown and will be updated.
Fitted with a Franklin O-425-1, 245 hp (183 kW) powerplant, the S-52-1 (1949 variant) established the World's speed record of 129.1 mph (207.8 km/h) and the World's altitude record of 21200 ft (6462 m).
Source: Alex, Ralph. "Helicopters from 'A to Z'". American Helicopter Society Newsletter, Vol. 7 1961. Page 16.