NORFOLK, Va. -- An entire class of Navy ships designed to quickly move troops and equipment around the world has major problems that could prevent them from accomplishing that mission.

That's the conclusion of a new report from the Defense Department Inspector General.

The catamaran-style expeditionary fast transport ships, according to the report, were supposed to be able to carry 1.2 million pounds of cargo for 1,200 nautical miles at an average speed of 35 knots, or about 40 miles per hour. But initial testing showed the ships were only able to carry that amount for 769 nautical miles at an average speed of 31 knots.

The aluminum ships have a large cargo space and a flight deck for helicopters and drones. They were designed to respond to a wide variety of military missions and could also be used in evacuations and disaster relief.

Since 2008, the Navy has purchased 12 expeditionary fast transport vessels from defense contractor Austal USA. By last summer, Austal had delivered eight of the ships. The other four are expected by the end of the 2019 fiscal year.

So far, the Navy has spent about $2 billion on the program, and the report says it may have to spend even more to fix all the problems that inspectors found with the ships that already have been delivered.

The first ship in its class, the USNS Spearhead, is based at Joint Expeditionary Base Little Creek-Fort Story in Virginia Beach and is currently deployed on a humanitarian and goodwill mission to Latin America. The ships are operated by 26 civilian mariners who report to Norfolk-based Military Sealift Command. The vessels have airline-style seating for up to 312 others and berthing for an additional 104.

The problems with speed and distance weren't the only ones the IG report, released on Wednesday, identified. It cited 28 deficiencies, all but nine of which could have a significant impact on missions.

One major problem had to do with controls that involve the secure exchange of information.

"Cybersecurity vulnerabilities could potentially lead to hackers disabling or taking control of systems, preventing the EPF vessel from accomplishing its missions," the report said.

Another problem inspectors found with the ships is that equipment cannot be transferred from one to another as expected, especially in rougher seas.

"The EPF vessel could only conduct vehicle transfers when waves were 0.3 meters or less, a condition normally only found in protected harbors," the report says.

The Navy said in a response to the report that it is working to correct problems in ships that have already been delivered.

©2018 The Virginian-Pilot (Norfolk, Va.)