Sikorsky Aircraft, a unit of United Technologies Corp, won an initial $1.24 billion contract to develop and build six new US Presidential helicopters, the first step towards a fleet of 21 new aircraft by 2023, the Pentagon announced.

The award capped years of efforts by the US Navy to replace the current fleet of ageing Marine One helicopters, also built by Sikorsky, some of which have ferried the President and other top officials since 1974. Sikorsky has built all Presidential helicopters since 1957, when Dwight Eisenhower became the first US President to regularly use helicopters.

The total value of the new programme is expected to be about $3 billion, said Marty Hauser, Director of Government Communications for United Technologies. Lockheed will be the key subcontractor to Sikorsky on the new programme, which is based on the Sikorsky S-92 helicopter that is already used by 10 nations for their head of state missions.

“For 57 years, our company has been trusted with the critical responsibility of building and supporting a safe and reliable helicopter fleet for the President of the United States,” Sikorsky President Mick Maurer said in a statement. “We stand ready to deliver the next Marine One, the world’s most advanced executive transport helicopter.”