This is a Momentous Technology milestone.
This was the first time a gas turbine engine had been used to apply power through a conventional helicopter gearbox. A Kaman K-225 was used as the base aircraft, and used a Boeing 502-2 (YT50) engine.
Gas turbine engines have subsequently become the de facto engine technology for the majority of VTOL aircraft other than small aircraft.
Source: Smithsonian National Air and Space Museum | Kaman K-225