* New weapons. Block 4 will support the
Stormbreaker smart glide bomb (formerly known as Small Diameter Bomb II) and allied weapons such as the UK’s
ASRAAM and
Meteor missiles, Turkey and Lockheed Martin’s
Standoff Missile (SOM-J), and the Kongsberg/Raytheon
Joint Strike Missile, a new missile capable of land attack and anti-ship missions.
* Electronic warfare and communications updates. The F-35 will receive 11 radar and electro-optical updates and 13 electronic warfare updates, allowing the jet to detect enemies sooner and jam them.
* Ground control collision avoidance system (GCAS). Pilot disorientation is a serious issue in modern combat aircraft. Earlier this year, a F-35 was lost after Major Akinori Hosomi, an experienced pilot with the Japan Air Self Defense Force,
lost situational awareness and flew his aircraft into the Pacific Ocean. GCAS will use the aircraft’s onboard sensors to detect when the aircraft is on a dangerous path to crashing. The system will warn the pilot and, if the warnings aren’t heeded, will actually take control of the aircraft and place it on a safe flight path. GCAS would have saved the pilot and aircraft in the April 2019 incident.
* Extended fuel tanks. The F-35’s range has come into criticism in recent years, as the U.S. fighter fleet faces the prospect of long-range combat against other major powers. Block 4 would add an additional 600 gallons of fuel carried in external fuel tanks. That isn't ideal, as even minor changes to the external appearance of the F-35 will compromise the airplane’s carefully crafted anti-radar profile, but short of magically finding room inside the plane for more fuel, it's pretty much the only solution to the range problem.
* Unmanned teaming. The U.S. Air Force, and undoubtedly other air forces, are looking into the idea of pairing F-35s with unmanned aircraft to handle complex threat environments. Drones like the XQ-58 Valkyrie, which the USAF wants to buy to experiment with, could probe enemy defenses, carry jammers, and carry out diversions to allow the manned to get close enough to the target to safely attack it. Such use of drones could dramatically increase the effectiveness of a F-35 fighter without teaming it with other, equally expensive F-35s.
* Other upgrades. According to a slide shared by Aviation Week & Space Technology's Stephen Trimble from the Paris Air Show, other system upgrades include an increased ability to help shoot down ballistic missiles, probably including using the Distributed Aperture System of infrared cameras to detect the heat plume of a missile taking off. The F-35 will also get open architecture improvements, likely to help speed the integration of future upgrades, the ability to work alongside naval and ground units, and other classified improvements.
Finally, Block 4 will apparently include classified improvements from Lockheed Martin’s famous “Skunk Works,” responsible for such aircraft as the SR-71 Blackbird and U-2. Exactly what those improvements are remains to be seen, but they could include literally anything from jam-proof communications to laying the groundwork for adding a laser weapon to the F-35.