Northrop Grumman Corp.’s Bethpage unit has won a $68.8 million contract for 30 mm guns on the Navy’s fleet of littoral combat ships, the Department of Defense announced.

Twelve percent of the work, worth about $8.3 million, would be done in Bethpage, while Northrop units in Portsmouth, Virginia, and Huntsville, Alabama, would get the largest allocations at 45 percent and 18 percent, the Defense Department said.

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The Navy’s littoral combat ships are high-speed vessels that operate in coastal waters. They are used to intercept pirates, interdict smugglers and counter terrorists. The contract includes support for installation, maintenance and support.

Prototype ships tested when the Navy was selecting a contractor reached more than 50 mph.

The contract, which has options that could bring its cumulative worth to $812 million, is expected to be completed by July 2019, the Defense Department said.

Northrop was the only bidder on the competitive contract issued by the Naval Sea Systems Command in Washington, D.C.

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“We are delighted to have been awarded a contract to continue this important work,” Northrop said in a statement. The company is based in Falls Church, Virginia.