The US Air Force (USAF) will receive seven more F-35 Lightning II stealth fighters from Lockheed Martin in the third batch of the low-rate initial production (LRIP).

The $857m fighter acquisition by the air force is part of a larger contract of $2.1bn awarded by the US department of Defense to Lockheed for delivering a total 17 F-35s to the USAF, the US Marine Corps, the Netherlands and the UK.

The air force will pay $122.4m for each of the seven conventional take off and landing aircraft.

Previously, deals had been struck with Lockheed worth $517m in the first and second phase of LRIP for purchase of these stealth fighters.

Assembly of 14 crafts is underway. Eight development aircraft being tested while 11 more are to be delivered by end of 2009.

Lockheed plans to achieve the one-aircraft-a-working-day target by 2015 with the production of F-35s.

The F-35 is a supersonic, multirole, fifth generation stealth fighter capable of undertaking mature fighter programmes.

Three variants of the F-35s are expected to replace at least 13 types of aircraft in nine nations.