Lockheed Martin Corp (LMT.N) is close to signing a roughly $4 billion deal with the U.S. Defense Department for 43 more F-35 fighter jets that will lower the cost of the jet’s airframe by 2 to 4 percent, sources familiar with the program said.

The reduction is part of a drive by the company and other key F-35 suppliers to slash the projected $400 billion cost of developing and building 2,457 U.S. jets in coming years – and the $1 trillion in additional costs to operate and maintain them over 50 years.

Lockheed’s F-35 program manager Lorraine Martin and Air Force Lieutenant General Chis Bogdan this week both said the two sides were “close” to agreement for an eighth batch of F-35s. Neither disclosed details. […]