As the Navy plans for a buildup, a new report from the Government Accountability Office has found that the service underestimated the number of personnel needed to man and maintain its current ships.

"The Navy's process to determine manpower requirements — the number and skill mix of sailors needed for its ships — does not fully account for all ship workload," the GAO report says. "The Navy continues to use an outdated standard workweek that may overstate the amount of sailor time available for productive work."

The report recommends that the Navy reassess how it determines manpower requirements, examine the amount of work it takes to maintain ships when in port and identify how much it would cost to man a larger fleet.

While the report only looked at manning levels in the surface fleet, it raises larger questions about personnel needs across the whole Navy, particularly as the service seeks to grow its total number of ships by as much as 30 percent.

The Navy's newest force structure assessment calls for 355 ships — five more than what President Donald Trump has proposed.

In building up the fleet, the Navy likely will face manning challenges, the report says. At the same time, the Navy hasn't determined the number of personnel that will be needed to operate those additional ships.

"If you're talking 47 new ships added to fleet, that means an additional 15,000 personnel within the Navy," said U.S. Rep. Joe Courtney, D-2nd District. "There really is no proposal that I'm aware of about increasing the top line of Navy end strength to accommodate that."

It's not just about adding ships and submarines, you have to ensure there's enough personnel manning them and also have a coherent plan for maintenance, Courtney said.

When the Navy updates its five-year shipbuilding plan in fiscal year 2018, "is really where the path to 355 (ships) is going to have to be laid out," Courtney added. "That's really where I think the manning question will come up."

In the early 2000s, the Navy reduced crew sizes in an attempt to drive down personnel costs and increase workload efficiencies, an initiative called "optimal manning." The GAO report found that ship maintenance and operating costs, personnel costs and maintenance backlogs all increased during the optimal manning period (2003–12) and have continued to increase for most ship classes since the initiative ended.

The reduced crew sizes, along with longer deployments, contributed to decreases in the material condition and readiness of ships, the report says. In 2010, the Navy concluded that optimal manning did not have the intended outcomes.

The report came out a day after Adm. John Richardson, chief of naval operations, released a white paper that outlines his desire to build a bigger fleet more quickly and incorporate new technologies to compete with other countries.

j.bergman@theday.com