A Pentagon acquisition review panel in July confirmed system requirements of the U.S. Navy’s future MQ-25 Stingray unmanned refueling aircraft, according to a Government Accountability Office (GAO) report to Congress released this month. The report provides schedule and cost detail on the closely guarded program, which earlier called for a surveillance and strike platform.

The Pentagon’s Joint Requirements Oversight Council (JROC) validated the Navy’s two primary requirements for the MQ-25: that it be capable of operating from aircraft carriers and that it refuel other carrier-based aircraft, a mission now performed by F/A-18E/F Super Hornets. The Stingray will have “limited” intelligence, surveillance and reconnaissance (ISR) capability to detect and report on surface targets, but it will operate in “permissive” environments without being exposed to threats.

Navy leadership approved the MQ-25 acquisition strategy in April, the GAO said. The program consists of aircraft, control system and carrier segments. Between Fiscal Years 2017 and 2022, the service plans to spend nearly $2.5 billion to continue development of the carrier and control segments and begin development of the aircraft segment. Annual spending will increase from $89 million this year to $554.6 million in 2022.

The Navy originally identified the need for a carrier-based aerial refueling capability in 2000, according to a GAO timeline. On a separate track in 2010, the service sought information from industry on developing a stealthy, carrier-based unmanned aircraft, a requirement that three years later became the unmanned carrier-launched airborne surveillance and strike system (UCLASS). In January 2016, the Pentagon stopped the UCLASS program and directed the Navy to focus instead on developing an unmanned carrier-based aerial refueling system—or CBARS—which the service subsequently designated the MQ-25.

General Atomics Aeronautical Systems, Boeing, Lockheed Martin and Northrop Grumman have had Navy contracts since 2011 to study concepts for the air vehicle, originally under the UCLASS effort. Last September and October, the service awarded the four companies a total of $250 million in contracts to conduct risk-reduction work, and in April awarded them contract amendments to refine their concepts for what is now the MQ-25.

In late July, the Naval Air Systems Command released a draft request for proposals (RFP) to the four contractors. The service plans to release a formal RFP for the air vehicle by October, the GAO said. Following a “Milestone B” review scheduled for next summer, it will select one of the contractors to advance to the engineering and manufacturing development (EMD) phase.

The Navy expects that it will take six to eight years to develop the MQ-25 air vehicle from Milestone B to initial operational capability, the GAO said.

Analysts with the Pentagon’s Cost Analysis and Program Evaluation (CAPE) office were still in the process of developing an independent cost estimate for the MQ-25 air vehicle, according to the oversight agency. CAPE officials “explained that they had not yet completed their estimate, but they plan to have it done in time to support the Navy’s MQ-25 Milestone B review in the summer 2018,” the GAO said.