RAAF F-35As are currently fitted with Block 3F software and hardware. (ANDREW MCLAUGHLIN)

The US Department of Defense has let two major contracts for the development of the Block 4 upgrade of the Lockheed Martin F-35 Lightning II.

Lockheed Martin was awarded a US$712.5m (A$1.03bn) contract for the development of “advanced hardware in support of the F-35 Lightning II Technology Refresh 3 (TR3) System.” The TR3 will form the basis of the hardware upgrade for Block 4, primarily for the aircraft’s avionics.

From 2023, Block 4 will be the follow-on system to the current Block 3F iteration which is being delivered on current build F-35s, and retro-fitted to older aircraft. Block 3F is the baseline capability from which most F-35 operators, including Australia, will declare an initial operational capability (IOC).

As part of what the JSF program office (JPO) and Lockheed Martin call the F-35 continuous capability and development delivery (C2D2) program, Block 4 will be delivered in serval increments dubbed 4.1, 4.2, 4.3 and 4.4, each of which will have increasingly enhanced software loads and additional capabilities added.

Also awarded as part of the Block 4 upgrade was a US$230.1m (A$332.2m) contract to Pratt & Whitney for the “testing support for the… Block 4 Flight Test Program” for the US and the eight JSF partner nations. The contract includes provisions for technical engineering, flight test support, special tooling and test equipment, flight test spare and repair parts. 

Both Pratt & Whitney and rival General Electric have proposed enhanced variants of their F-135 and F136 engines respectively, although P&W is currently the only engine supplier to the JSF program.