Inside Block 4—The Mostly Secret Plan For Making The F-35 Fighter Even More Lethal

The F-35 fighter is the most advanced tactical aircraft currently in production anywhere. Its low-observable (“stealth”) features give the plane a radar signature similar to that of a steel golf ball, and its onboard sensor fusion gives the pilot unprecedented situational awareness.

Designed to perform a diverse array of missions, from air-to-air combat to precision bombing to radar jamming to intelligence gathering, the F-35 is so capable that 16 countries have signed up to buy it—and more will follow.

However, the F-35 needs to maintain its fighting edge over potential enemies through 2070. No matter how imaginative its original configuration may have been, periodic upgrades of the fighter’s technology will be required. The upgrades are needed not only to perform new missions, but to assimilate better technology for accomplishing existing tasks.

The Joint Program Office has begun executing the most ambitious round of upgrades since the fighter’s inception two decades ago, called Block 4. Block 4 is referenced frequently in government reports and technical literature, but writers often talk around it because the substance of the upgrades is classified.

My purpose here is to describe in simple terms what Block 4 entails, to the extent that can be described publicly. I should note at the outset that several companies involved in that effort, including airframe integrator Lockheed MartinLMT
, contribute to my think tank.

Block 4 will introduce over 75 major upgrades into the fighter, which is operated in different variants by the Air Force, Navy and Marine Corps. Most of these upgrades involve modifications to electronic hardware and software.

However, before these changes can be implemented, the fighter’s core processor and memory unit must be improved. This is accomplished via an upgrade called Technology Refresh 3, or TR-3. The fighter’s previous computing system, TR-2, is not adequate to support the capability upgrades included in Block 4.

TR-3 is described by people close to the effort as the “IT backbone” for all future improvements. It thus is pivotal to implementing Block 4.

TR-3 is being installed in all new production aircraft including the Lot 15 aircraft being delivered today, and will be retrofitted onto fighters already in the fleet back to Lot 10. The retrofits require about 14 days of downtime and will be performed by Lockheed field teams during scheduled maintenance.

In addition to greatly increasing the F-35’s processing power and computer memory, the technology refresh will migrate to an open-system architecture designed to facilitate further upgrades in the future. One advantage of this approach is that it minimizes the likelihood of users becoming dependent on specific vendors for system improvements.

But once TR-3 is underway, the hard part begins, because it isn’t enough to improve other onboard hardware and software to stay ahead of what China or Russia might be doing today. The F-35 needs to be enhanced to surpass the capabilities those countries might be fielding in ten or twenty years.

So, the Block 4 upgrades enabled by TR-3 are quite imposing, increasing the range and diversity of weapons that can be carried, plus the sensitivity of sensors used to detect, track and engage targets. Most of the new weapons, 17 in all, are “kinetic” weapons such as missiles, but they also include non-kinetic systems that use clever software and waveforms to jam or confuse enemy warfighting systems.

Upgrade 4 also enhances networking capability with other tactical systems to enable what the military calls integrated, long-range “kill webs.” The phrase implies broad coverage of multiple warfighting domains made possible by weaving together the capabilities of scattered operators, not all of them in the air.

The military is generally mum on details here, but at the very least a kill web requires the fusion of sensor inputs from diverse sources, plus long-range weapons capable of exploiting the resulting gains in tactical awareness. This all must unfold in seconds to be effective, dictating the need for continuous, secure and high-capacity connectivity across the battlespace.

Thus, while the budget lines supporting Block 4 are mainly concerned with upgrades organic to the fighter itself such as an improved panoramic cockpit display, they fit into a vision of networked warfare that transcends any particular platform. The fighter becomes a node in a broader warfighting architecture.

Block 4 will demand more power, cooling and thermal control than are resident on the baseline configurations of F-35. Some upgrade of the fighter’s main engine will be required, either in the form of an improved F135 powerplant or a new engine. The Joint Program Office has not finalized the long-term performance requirements that will drive how the fighter’s propulsion system is improved.

As with any complex military project, the budgetary aspects of Block 4 are not so easy to grasp. A recent report by the Government Accountability Office noted that the cost of Block 4 upgrades to the F-35 fleet had risen to an estimated $15 billion across over a dozen years.

However, a careful reading of the GAO report reveals that the cost increases are largely due to capturing early costs incurred by the effort but not included in previous estimates, and by a decision to add 25 more capabilities to the package of upgrades.

Those of us without clearances may never know what some of the added capabilities are because they are grounded in classified assessments of overseas military developments and the appearance of new missions not anticipated at the F-35’s inception.

There isn’t much doubt, though, that if the F-35 is to stay on the cutting edge of warfighting capability, Block 4 is indispensable. That presumably is understood not only in Congress, but among the many allies who plan to operate the fighter through mid-century.

F-35 program participants who contribute to my think tank include BAE Systems, Lockheed Martin, and Raytheon Technologies
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