Lockheed Martin Corp. has protested a $3.74 billion Navy contract awarded to Northrop Grumman Corp. to build unmanned spy-planes.

Lockheed said it decided to file the protest with the Government Accountability Office after a Navy briefing showed the Lockheed proposal met the Navy’s technical requirements and cost significantly less, said Lockheed spokeswoman Tierney Helmers.

The Navy countered Monday that it was confident that the acquisition process was fair, and that Northrop’s proposal provided the “best overall value.” Northrop’s Global Hawk drone, already being flown by the Air Force in Iraq and Afghanistan, beat out offerings by Boeing Co., as well as Lockheed.

Northrop won the contract at the end of April.

This is the second protest Northrop is facing on a recent defense contract. In February, a consortium of Northrop and the European Aeronautic Defence and Space Co. beat out Boeing for a $40 billion contract to supply the Air Force with its next generation air tanker. Boeing filed a protest with the GAO on that award as well.

Shares in Northrop closed down 56 cents to $74.44 Monday.