XM121 30mm HE-P Round: US Army Adapts Existing Munitions for Counter-UAS Role
The US Army Capability Programme Executive for Ammunition and Energetics is repurposing existing 30 mm, mortar and artillery natures with proximity fuze technology to engage Group 1–3 Uncrewed Aerial Systems at a fraction of missile interceptor cost.
Technical Summary
The US Army is evaluating the XM121 High Explosive Proximity (HE-P) round, a 30 mm projectile fitted with an electronic proximity fuze, as a low-cost counter-Uncrewed Aerial System (C-UAS) effector. The programme, disclosed at a Defense One conference on 26 March 2026, represents a doctrinal shift away from expensive missile-based intercept solutions toward kinetic defeat of Group 1–3 UAS using existing gun platforms and ammunition natures.
The XM121 is designed for the M242 Bushmaster chain gun mounted on the M2A3/M2A4 Bradley Infantry Fighting Vehicle (IFV). The round employs a radar or radio-frequency proximity fuze that triggers detonation when the projectile passes within a pre-set miss distance of the target, eliminating the requirement for a direct hit. The high-explosive warhead — likely containing an RDX/TNT-based composition with a Net Explosive Quantity (NEQ) of approximately 30–50 g TNT equivalent per round — generates a lethal combination of blast overpressure and pre-formed or natural fragmentation sufficient to defeat lightweight composite UAS airframes.
Beyond the 30 mm programme, the Army is examining whether existing 60 mm, 81 mm and 120 mm mortar natures, as well as 105 mm and 155 mm artillery rounds, can be adapted with airburst or proximity fuze capability for area-effect C-UAS engagement. The Mk 19 40 mm automatic grenade launcher is also under consideration as a C-UAS platform, leveraging its existing high rate of fire against slow-moving aerial targets.
Analysis of Effects
The XM121’s proximity fuze mechanism represents a significant advance over point-detonating (PD) fuzing for the C-UAS role. A PD-fuzed 30 mm round requires a direct hit on a target with a radar cross-section frequently below 0.01 m², yielding a probability of hit (Ph) in the low single digits per round. A proximity fuze expands the effective engagement envelope to a radius of several metres around the projectile flight path, increasing Ph by an estimated factor of 10–50× depending on fuze sensitivity and target geometry.
The lethal radius (LR) of a single 30 mm HE-P detonation against a Group 1 UAS (sub-10 kg) is estimated at 3–5 metres, based on fragmentation density and blast overpressure thresholds required to compromise lightweight composite structures. Against Group 3 UAS (up to 600 kg), multiple hits or a higher-calibre airburst round would be required to achieve mission kill.
The 30 mm HE-P round is assessed as Hazard Division 1.2, Compatibility Group G (HD 1.2G) under NATO AASTP-1 classification, consistent with existing 30 mm HE natures containing a secondary explosive fill with a fuze that possesses two or more effective protective features. Storage and transport requirements align with current 30 mm ammunition logistic chains.
Personnel and Safety Considerations
Ammunition Technicians (ATs) and Explosive Ordnance Disposal (EOD) operators should note that proximity-fuzed munitions introduce specific handling and disposal considerations not present with conventional PD-fuzed 30 mm natures. The electronic proximity fuze contains a radio-frequency emitter/receiver that may be susceptible to electromagnetic interference (EMI), requiring compliance with STANAG 4235 (Electromagnetic Environmental Effects on Ordnance) during storage and transport.
Failed-to-function XM121 rounds will present an elevated unexploded ordnance (UXO) hazard compared to PD-fuzed equivalents. The proximity fuze’s electronic arming and firing chain may leave the round in an indeterminate fuze state following a miss, requiring EOD render-safe procedures (RSP) that account for both the electronic fuze and the sensitive secondary explosive fill. Cordon distances for individual 30 mm UXO should follow national EOD manuals, with a minimum recommended clearance of 100 metres pending fuze state assessment.
Data Gaps
AI-assisted technical assessment based on open-source material. Not a formal intelligence product. Classification: Open Source | AI-Assisted Technical Assessment.
ISC Commentary
Further analysis pending.