The US Navy has reportedly placed orders for two more Sikorsky CH-53K system demonstration test article (SDTA) aircraft to allow the US Marine Corps (USMC) to carry out trials for operational assessment.
This follows the navy's previous $435m agreement in June 2013 for four CH-53K aircraft.
The US Navy was quoted by Flightglobal as saying that the additional orders do not come in the wake of modifications to the design or production of the heavy-lift helicopter.
"The procurement ... is targeted at maturing production processes," the US Navy said, adding that the SDTAs would assist in ensuring the readiness of production, systems, facilities, tooling, test equipment and inventory and supplier management.
Being manufactured as part of the navy's plans to procure 200 aircraft, the first production-representative CH-53K heavy-lift helicopter is scheduled for delivery around September 2016.
Sikorsky has already assembled one of the test aircraft and is currently undergoing ground tests, while three of them are being assembled.
With a capacity to carry over 27,000lb of external load in extreme weather conditions, the 39.9t CH-53K helicopters are powered by General Electric GE38-1B engines, and would replace the existing CH-53E Super Stallions in 2019.
Sikorsky will carry out final assembly work on the SDTA at its facility in West Palm Beach, Florida, US.
Image: Sikorsky's CH-53K ground test vehicle (GTV). Photo: courtesy of the Sikorsky Aircraft Corporation.