WASHINGTON -- Pratt & Whitney, a unit of United Technologies Corp, on Tuesday said it finalized a $1 billion deal with the Pentagon for a fifth batch of engines for the single-engine Lockheed Martin Corp F-35 fighter jet.

The contract covers 35 engines, including 32 to be installed in F-35 warplanes, and three spares, said Pratt spokesman Matthew Bates.

The company reached an initial agreement with the Pentagon on the fifth engine contract in early February.

Chris Flynn, who heads Pratt's F135 and F119 engine programs, said the company continued to work with the U.S. Defense Department to drive down engine costs and accelerate the contracting cycle for future production agreements.

"As we move forward in the program, the key factors in driving down cost will be to increase the ramp rate and volume of engines," Flynn said in a statement. "Achieving greater program stability will help us to progress further down the cost curve to meet the price reduction objectives on the program."

Pratt has delivered 98 production engines for the F-35 program to date.