U.S. Navy following U.K on IRST for fighters

The U.S. Navy expects to award contracts soon for a longer-range version of the AIM-9X Sidewinder, known as Block III. Not only will it be a major change to the AIM-9X—retaining only the seeker, optical target detector and data link of the Block II weapon—but its development is starting before the Block II has finished operational tests.
The Block III is associated with the Navy's effort to fit the F/A-18E/F Super Hornet with a Lockheed Martin infra-red search and track (IRST) system. The two systems are complementary, improving the ability of Navy fighters to operate in what a Boeing engineer calls an “RF (radio frequency)-denied environment” that will challenge X-band systems such as fighter radars and the seeker of the AIM-120 Advanced Medium Range Air-to-Air Missile (Amraam).
With these developments, the U.S. Navy is following the lead of other air arms—notably, the Royal Air Force—in investing in non-RF sensors and weapons that work far outside the within-visual-range envelope. One key technology is better processing that has greatly improved the performance of IRST.
aviationweek