The Government Accountability Office has advised the U.S. Navy to review funding and technology resources for the Unmanned Carrier-Launched Airborne Surveillance Strike aircraft development program.

GAO said Monday the delay of Navy’s UCLASS program was caused by a debate over whether the future carrier-based drone’s primary mission should be surveillance or strike.

The agency believes a strike role would require more funds.

According to GAO, the military branch expects to spend at least $3 billion over the next five years to build the aircraft, carrier and associated systems.

The Navy awarded a total of $60 million to Boeing, General Atomics Aeronautical Systems, Lockheed Martin and Northrop Grumman for UCLASS preliminary design work.

GAO also urged the Navy to develop a business case to demonstrate that available program resources match with requirements before the service awards an aircraft development contract.