The Government Accountability Office (GAO) urged the Navy Aug. 4 to hold off on procuring a new version of the Arleigh Burke-class (DDG-51) guided-missile destroyer until the ship’s design is further along.

The Navy plans to buy the first DDG-51 Flight III ship in fiscal year 2016 and ask Congress in February for authority to pursue a multi-year procurement for nearly half of its Flight III ships. But the Navy will be doing so without having completed the detail design, an approach that “portends risk in the future,” the GAO wrote in a new 72-page report. The congressional watchdog agency recommended that the Navy wait until at least FY 2017 to procure the lead ship.Underway operations.

In response to a draft of the report, the Department of Defense disagreed that the procurement should be delayed, saying the Navy expects to understand the ship’s design challenges before it starts construction. In addition, DoD wrote, delaying the lead ship “could impact the ability to meet the validated initial operational capability date [of 2023] and create risk to fulfilling the joint warfighters’ needs.”

The Navy plans to spend more than $50 billion over the next decade to design and build 22 Flight III destroyers, an upgrade from Flight IIA ships. Flight III ships will include the new Raytheon [RTN] SPY-6 air-and-missile-defense radar and improvements to the Lockheed Martin [LMT] Aegis combat system.

Integrating the radar “will require extensive changes to the ship’s hull, mechanical and electrical systems,” the GAO wrote. “For example, the ship’s deckhouse must be modified because the SPY-6 radar is considerably deeper and heavier than the legacy DDG 51 radar.”

Naval Sea Systems Command (NAVSEA) said in an April pre-solicitation notice that it intends to issue the request for proposals for the lead ship to General Dynamics [GD] Bath Iron Works. General Dynamics and Huntington Ingalls Industries [HII] are both working on the Flight III design.