Following a series of Iranian and Houthi-linked attacks against bases and infrastructure of the U.S.-led coalition in the Middle East, the U.S. Air Force (USAF) has issued an Urgent Operational Requirement (UOR) for air-defense guns capable of engaging threats ranging from drones to cruise missiles.

According to the official USAF statement, the Ground-Based, Medium-Caliber Gun Weapon System program is seeking a weapon "that fires affordable munitions, enables defense against air and missile threats with an initial focus on subsonic cruise missiles (CM) and Unmanned Aircraft Systems (UAS) to provide persistent defense in support of United States Air Force assets."

The USAF Request for Information (RFI) does not specify a caliber for the new system, although the "medium-caliber" designation points to a weapon in the 20-50 mm range. Baseline parameters include probability of kill (PK) against subsonic cruise missiles and against Group 1 through Group 5 unmanned aerial vehicles, spanning small drones up to large UAVs operating above 18,000 feet (approximately 5,500 m).

On the sensor side, the USAF has requested that the new system be closely integrated with "organic sensor capability and phenomenology - integrating the right mix of radar, electro-optical, infrared, or radio-frequency sensors - to ensure reliable target acquisition and tracking across varying weather conditions, environments, and countermeasure scenarios." The system must also be able to defeat drone and missile swarm attacks and be rapidly deployable in austere environments, while the USAF is also seeking a portable solution with "a lightweight, modular, and transportable footprint."

Drawing on lessons learned in the Middle East (and from the experience of the Israel Defense Forces, IDF, in particular), the service is placing strong emphasis on the need to "optimize munition performance versus munition cost and gun capability, ensuring that the interceptor's velocity, maneuverability, and terminal effects are maximized without driving the cost-per-engagement to unsustainable levels or exceeding the physical constraints of the host platform." A near-term solution could come from the U.S. Army, which is planning live-fire tests of Northrop Grumman's XM913 BUSHMASTER 50 mm chain gun to meet a broadly similar requirement. Another option already in service is the U.S. Marine Corps' (USMC) Marine Air Defense Integrated System (MADIS), which, however, does not yet cover the full scope of the identified operational requirements.

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