The contract follows the previously awarded $3.5bn system development and demonstration (SDD) contract to Sikorsky in April 2006, for the delivery of five developmental test aircraft and two ground static test airframes.
Under the $435m cost-plus-incentive modification contract, Sikorsky will develop four CH-53K system demonstration test article (SDTA) aircraft for use by the USMC to test during operational evaluation.
NAVAIR heavy lift helicopters programme manager Colonel Robert Pridgen said that the CH-53K SDTA aircraft was critical to sustaining the future missions of the Marine Air/Ground Task Force.
"We are well on our way to making the CH-53K a reality for our marines and our naval fleet," Pridgen added.
Capable of carrying more than 27,000lb of external load in extreme weather conditions, the CH-53K helicopters are being developed to replace the existing CH-53E Super Stallions in 2019.
Sikorsky CH-53K programme vice-president Dr Michael Torok said: "The four SDTA aircraft are based on the configuration of the fourth and final flight test aircraft currently being assembled on the prototype production line."
The first CH-53K SDTA aircraft is scheduled to be delivered in 39 months while the last in by the end of March 2017, with the USMC then starting the operational evaluation.
Final assembly work of the SDTA aircraft will be conducted at the company’s Florida assembly and flight operations facility in West Palm Beach, US.
Image: Officials during SDTA contract signing ceremony. Photo: courtesy of Sally Wise.