WASHINGTON — The Pentagon on Tuesday announced a $34 billion F-35 contract with Lockheed Martin, the largest contract yet for the defense company's costly fighter program.

The deal is for the delivery of 478 of the aircraft.

The F-35, the crown jewel in the defense giant's portfolio, has become one of the most challenged programs in the history of the Department of Defense. The laundry list of setbacks includes faulty ejection seats, software delays and significant helmet-display issues. The program had an initial acquisition cost of $406.5 billion.

Yet the Pentagon touted reduced costs and a quicker timetable in its announcement Tuesday.

"This agreement achieves an average 12.7% cost reduction across all three variants and gets us below $80 million for a USAF F-35A by Lot 13 – one lot earlier than planned," Air Force Lt. Gen. Eric Fick, F-35 program executive officer, said Tuesday.

Lockheed Martin's fifth-generation F-35 comes in three variants, the F-35A for the U.S. Air Force, F-35B for the U.S. Marine Corps and F-35C for the U.S. Navy.

"The $34 billion agreement for F-35 low-rate initial production lots 12-14 includes the delivery of 478 F-35 aircraft," Ellen Lord, undersecretary of Defense for acquisition and sustainment, said Tuesday at the Pentagon.

The contract announced Tuesday covers three lots of orders: 12, 13 and 14. Each one is essentially a batch of aircraft. The deal for lot 12 was for 149 jets, 160 for lot 13 and 169 for lot 14, for a total of 478 fighters for the U.S. military and allied partners.

Lord reiterated the department's commitment to the F-35 program at the Pentagon.

"I have full faith and confidence in the F-35 program and our ability to delivery F-35 combat capability anywhere in the world. Make no mistake, the F-35 is the world's most advanced, lethal and interoperable aircraft ever developed," she said.