Sikorsky Aircraft Corp., a Lockheed Martin Co., Stratford, Connecticut, is awarded a not-to-exceed $525,000,000 firm-fixed-price, cost-plus-fixed-fee, cost reimbursable indefinite-delivery/indefinite-quantity contract to provide highly specialized non-recurring engineering, integration, and flight-test support for the development and modernization of the Y/CH-53K Heavy Lift Helicopter program. Efforts include the design, development, testing, verification, and validation of product improvements, as well as the integration and qualification of advanced technologies to enhance aircraft capability, performance, and reliability for the Marine Corps, Navy and a Foreign Military Sales customer. Work will be performed in Stratford, Connecticut (65.2%); West Palm Beach, Florida (19.93%); Fort Worth, Texas (4.79%); Trumbull, Connecticut (3.16%); King of Prussia, Pennsylvania (1.43%); Rochester, Minnesota (1.12%); and various locations within the continental U.S. (4.37%), and is expected to be completed in June 2031. No funds will be obligated at the time of award; funds will be obligated on individual orders as they are issued. This contract action was not competed. Naval Air Systems Command, Patuxent River, Maryland, is the contracting activity (N0001926D1005).