The Pentagon says more testing is required to demonstrate that the 25mm automatic cannon mounted internally on the F-35A variant of the Joint Strike Fighter is indeed now an effective weapon. Various software and hardware issues had long left the stealthy jets unable to shoot straight, but fixes intended to resolve them have been implemented.
New questions about the actual effectiveness of the F-35A’s internal gun emerged last month after the Project on Government Oversight (POGO), an independent nonprofit, published a heavily redacted declassified copy of a report on the Joint Strike Fighter program from the Pentagon’s Office of the Director of Operational Test and Evaluation (DOT&E). POGO obtained the document, which is dated February 2024, via the Freedom of Information Act (FOIA) and provided its own analysis of the contents. The report also underscored long-standing maintenance and logistics challenges that have contributed to historically low readiness rates across all variants of the F-35 and that could have worrisome impacts on future combat operations. The War Zone has explored those issues and their broader ramifications in detail in a past feature.
“The F-35 lethality assessment suffered from the inability of the F-35’s gun to hit the targets because of design and installation issues,” according to an unredacted section of the February 2024 DOT&E report that POGO obtained.
For context, each F-35A has a four-barrelled 25mm Gatling-type cannon, designated the GAU-22/A, mounted internally in a space above the aircraft’s left engine intake. The gun has a rate of fire of 3,300 rounds per minute and feeds from a 180-round magazine. A flush-mounted door opens when the gun is fired and closes when it stops to maintain the jet’s stealth signature. The F-35B and C variants do not have internal guns, but can carry GPU-9/A gun pods that contain a GAU-22/A and 220 rounds of ammunition.
It is no secret that problems tied to how certain symbology was presented to pilots through their helmet-mounted displays (HMD) had prevented all three F-35 variants from employing their guns effectively in the past. F-35s lack a traditional heads-up display (HUD) in their cockpits. The information a pilot would typically get from a HUD is instead projected onto the visor of their helmet.
The design of the internal mount for the GAU-22/A on the A version of the F-35 was also found years ago to have been so badly misaligned that it not only negatively impacted accuracy, but also caused physical damage to the aircraft from firing the gun. Additional concerns about cracking on the F-35A as a result of gun use have also surfaced in recent years.
You can read more about the F-35’s gun-related woes in detail here.
“After working with the Air Force and our industry partners we can report that the gun has been improved and is effective,” Russ Goemaere, a spokesperson for the F-35 Joint Program Office (JPO), had told The War Zone in March of this year. “We continue to work with industry, the Services, and our international partners for further improvements and to maximize effectiveness and lethality at the tactical/operational level.”
“The F-35 JPO made changes to hardware and software resulting in improved and effective gun operations,” Goemaere told The War Zone again last month in response to questions about the contents of the February 2024 DOT&E report.
“Operational testing of the F-35A/B/C gun systems occurred during F-35 Initial Operational Test and Evaluation [IOT&E]. The majority of this testing was in 2018 and 2019,” a U.S. defense official also told The War Zone in response to a question about when the “F-35 lethality assessment” referred to in the DOT&E report actually occurred.
“Operational testing of the F-35A/B/C gun systems with the latest iteration of fixes is planned, but has not occurred. DOT&E does not yet have data or reports that would alter the observations in the IOT&E report,” that same U.S. defense official added when asked about whether DOT&E currently agrees with the F-35 JPO’s current assessment of the effectiveness of the F-35A’s gun.
The effectiveness of the F-35A’s internally mounted gun has been a particular talking point with regard to the U.S. Air Force’s ongoing plan to retire the venerable A-10 Warthog ground attack jet and its famed 30mm GAU-8/A Avenger cannon. The A variant of the Joint Strike Fighter has been presented as the primary replacement aircraft. A separate and equally heavily redacted DOT&E report regarding still highly controversial comparison testing of the F-35A and the A-10C that occurred between 2018 and 2019 did refer to a need to “fix the F-35A gun,” but any further context was censored. POGO also obtained that report, which is dated February 2022 and had been effectively buried, via FOIA and subsequent litigation, and published it last year.
Effective or not, the GAU-22/A inside the F-35A with its 180 rounds of ammunition (which equates to just over three seconds of total firing time) cannot be directly compared in any way to the A-10’s legendarily huge GAU-8/A, which feeds from a 1,174-round magazine. The 30mm rounds the GAU-8/A fires are much larger than the 25mm ones that the GAU-22/A spits out, too. It is worth noting that the Avenger caused serious problems during the initial development fielding of the A-10, as you can learn more about here and in the video below.
The F-35A’s ammunition load for its gun is small, even in comparison to that of other stealthy and non-stealthy jets in U.S. service today. The M61 Vulcan cannons on U.S. Air Force F-16C Vipers and F-22 Raptors, for instance, have 500 and 480 rounds of 20mm ammunition to go along with them, respectively. The GAU-22/A’s 25mm rounds are bigger than the 20mm shells that M61s fire.
Questions have also been raised about the utility of available ammunition for the GAU-22/A. The primary operational round that all F-35s fire from their guns, whether they be internally mounted or in pods, is the PGU-48/B, referred to as a Frangible Armor Piercing (FAP) type. It is a kinetic round designed to damage/destroy targets through force of impact. The “frangible” tungsten penetrator inside also breaks up after hitting its mark to create deadly shrapnel. Despite its lack of explosive or incendiary elements, the PGU-48/B is said to be effective against aircraft, as well as armored vehicles and soft-skinned ground targets, according to the manufacturer, Germany’s Rheinmetall. What demonstrated effects the rounds may have against enemy personnel are unclear.
At around $131 dollars per round, the PGU-48/Bs are also expensive. The price point for a single 20mm PGU-28A/B semi-armor-piercing high-explosive incendiary cartridge, the main ammunition type for Vulcan cannons in Air Force jets, is around $34.
There remains a possibility that other 25mm ammunition types, such as high explosive and/or incendiary rounds, could be certified for use in the GAU-22/A in the future.
The close air support mission, even when performed by the A-10, is ever more about the employment of precision-guided munitions rather than strafing runs. The Air Force’s argument for retiring the Warthogs, a process that is now very much underway and looks set to be completed by the end of the decade if not well before then, has been centered on this reality. A-10s are still flying combat missions, including just this week in Syria.
At the same time, a working gun can still be an important tool for tactical aircraft to have in various circumstances. An accurate aerial gun offers the ability to provide even more focused fire on a target, and even more limited risk of collateral damage than most precision munitions, which can be particularly useful for supporting ground forces in dense urban environments. In air-to-air combat, the expectation is that traditional dogfights will become increasingly uncommon, especially for stealthy jets like the F-35 with its still-growing array of other advanced capacities. At the same time, visual-range aerial engagements could still occur in future conflicts, including during lower-end missions in dense airspace with tight rules of engagement or in high-end fights with large volumes of enemy and friendly forces operating in relatively constrained battlespaces.
Guns continue to provide immediate backup firepower for tactical jets should they run out of other munitions, in general. This was just recently highlighted by new details about the U.S. military’s contribution to the defense of Israel against incoming Iranian threats back in April. At least one Air Force F-15E Strike Eagle crew switched to their Vulcan cannon after they ran out of missiles while swatting down drones, though they were unable to score any gun kills.
In the meantime, DOT&E says it is still waiting to see the data showing that F-35A pilots can effectively do the same if necessary.
Contact the author: joe@twz.com