This is a Notable Operational milestone.
S-48 was the Sikorsky model number assigned to the type and R-5 the military designation. The XR-5 designation correctly refers to the experimental ('X') nature of the prototype. The aircraft was flown by company Chief Test Pilot Les Morris. Igor Sikorsky and Edward Ketzenberger were the patent holders for the design.
Source: "The Helicopter History of Sikorsky Aircraft", Don Fertman, VERTIFLITE May/June 1984, Page 17