M9 Armored Combat Earthmover

The M9 Armored Combat Earthmover (ACE) is a tracked armoured engineer vehicle of the US Army. Its design goes back to the late 1950s. The first prototypes, called the Universal Engineer Tractor (UET), were built by Caterpillar and International Harvester in the early 1970s. Funding was slow to come, and full production began only when BMY won a contract in 1986. Around 500 had been built by the time the archive's source was written. The original UET requirement even included carrying troops, either in the bowl or in the small rear compartment.

Design

The front third of the vehicle is an earth bowl, closed at the front by a two-piece apron that serves as the dozer blade, with an ejector board to push material out. The single driver sits in a small armoured cab on the left, with the engine and transmission beside him. Most of the hull is hardened aluminium armour, with extra steel and laminate plate around the driver. Hydropneumatic suspension lets the driver raise or lower the front of the hull for scraping and dozing. A Cummins V-903 V8 diesel of 290 hp, with a Clark transmission and Twin Disc steering unit, gives about 48 km/h and a range of about 370 km.

Amphibious capability

The early M9s were designed to swim and to be air-dropped, and had a hinged door closing the rear compartment. Both requirements were later dropped. The rear door was removed, and the hull and components were strengthened with less concern for weight.

Service

The M9 saw combat in Operation Desert Storm. On 24 February 1991, engineers of the 299th Engineer Battalion used it to breach Iraqi sand berms and trenches at the start of the ground campaign.