US Army Evaluates Proximity-Fuzed Conventional Munitions for Counter-UAS Role: XM121 30 mm HE Proximity Round

Technical Summary

The US Army's Project Manager for Maneuver Ammunition Systems is evaluating existing conventional ammunition types for adaptation to the counter-Unmanned Aerial Systems (C-UAS) mission. The initiative, reported on 26 March 2026, focuses on leveraging proximity fuze technology to enable non-direct-hit engagement of small drones, reducing the cost-per-engagement from millions of dollars (guided missile interceptors) to hundreds of dollars (conventional ammunition).

The primary candidate identified is the XM121 30 mm High-Explosive Proximity (HE-P) round, designed for the M230 chain gun mounted on the AH-64 Apache and adapted for ground-based platforms including the Bradley Fighting Vehicle (M242 Bushmaster cannon). The XM121 incorporates an electronic proximity fuze that detonates the round when it detects a target within its lethal radius, eliminating the requirement for a direct impact on small, manoeuvrable targets.

Additionally, the Army is examining legacy 60 mm and 81 mm mortar ammunition and 105 mm/155 mm artillery projectiles for potential modification with proximity fuze capability or for deployment from UAS platforms as air-dropped munitions. The Mk 19 40 mm automatic grenade launcher is also under evaluation for C-UAS employment with modified fuzing.

Analysis of Effects

Proximity Fuze Mechanism

Proximity fuzes (also designated Variable Time or VT fuzes) operate by emitting a radio-frequency or optical signal and detecting the reflected energy from a nearby target. When the reflected signal exceeds a threshold corresponding to a pre-set activation distance, the fuze initiates the detonation train. Modern electronic proximity fuzes such as those in the XM121 use solid-state electronics to measure Doppler shift, enabling discrimination between target returns and ground clutter.

For a 30 mm HE-P round, the lethal mechanism against a Group 1 UAS (under 9 kg) is a combination of blast overpressure and pre-formed or natural fragmentation. The typical lethal radius of a 30 mm HE projectile against an unarmoured aerial target is estimated at 3–5 metres, significantly relaxing the accuracy requirement compared to a direct-hit round.

Munitions Under Evaluation

Hazard Classification Implications

The introduction of electronic proximity fuzes to munitions previously equipped with point-detonating (PD) or mechanical time fuzes has implications for Hazard Division classification. Under NATO AASTP-1 (implementing STANAG 4440), munitions fitted with proximity fuzes that contain their own power source may be reclassified to HD 1.2 (projection hazard rather than mass detonation) depending on the fuze safety architecture and the presence of all-ways-acting fuzing mechanisms.

Ammunition technicians and logistics planners must account for the storage and transport implications of any reclassification. HD 1.2 items require different QD separation from HD 1.1 items and may change the compatibility grouping from CG D to CG E or CG F depending on the fuze configuration. This affects Inter-Magazine Distance (IMD) calculations, transport documentation under ADR/RID, and ammunition accounting systems.

Personnel and Safety Considerations

For EOD and Ammunition Technical (AT) personnel, the adaptation of conventional munitions for C-UAS introduces several considerations. Proximity-fuzed rounds that fail to function against a target (blind rounds) present a specific hazard: the fuze may remain in an armed state with a live electronic circuit, increasing the sensitivity of the item to electromagnetic radiation. STANAG 4234 (HERO — Hazards of Electromagnetic Radiation to Ordnance) requirements become directly relevant for any dud proximity-fuzed round.

Mortar and artillery rounds modified for air-drop from UAS platforms present novel Render Safe Procedure (RSP) challenges. An unexploded mortar round found without its launch tube context may not exhibit the expected arming indicators, and the fuze state assessment becomes dependent on understanding the modified delivery mechanism. Standing EOD procedures for conventional mortar ammunition may require revision to account for UAS-delivered variants.

Under DSA 03.OME and equivalent NATO doctrine, any modification to the fuzing system of an existing munition requires a new safety and suitability assessment. The adaptation of legacy ammunition for an unintended role (C-UAS rather than ground targets) must demonstrate that the modified fuze performs within acceptable safety margins under STANAG 4187 (Fuzing Systems — Safety Design Requirements).

Data Gaps

AI-assisted technical assessment based on open-source material. Not a formal intelligence product. Image attribution noted where applicable.

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