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HandWiki. M9 Armored Combat Earthmover. Encyclopedia. Available online: (accessed on 15 June 2024).
HandWiki. M9 Armored Combat Earthmover. Encyclopedia. Available at: Accessed June 15, 2024.
HandWiki. "M9 Armored Combat Earthmover" Encyclopedia, (accessed June 15, 2024).
HandWiki. (2022, December 02). M9 Armored Combat Earthmover. In Encyclopedia.
HandWiki. "M9 Armored Combat Earthmover." Encyclopedia. Web. 02 December, 2022.
M9 Armored Combat Earthmover

The M9 Armored Combat Earthmover (ACE) is a highly mobile armored tracked vehicle that provides combat engineer support to front-line forces. Fielded by the United States Army, its tasks include eliminating enemy obstacles, maintenance and repair of roads and supply routes, and construction of fighting positions.

tracked vehicle ace earthmover

1. History

The M9 grew out of the Universal Engineer Tractor- "UET", a follow-on to 1958's All-purpose Ballastable Crawler (tractor) or "ABC".[1] By making a small tractor/scraper, it was possible to create a lightweight vehicle that could use local material as ballast. The weight was kept low enough to allow transportation in smaller cargo aircraft, to be air-droppable, and to allow the vehicle to float and swim. Initial development was between the Engineer Laboratory at Ft Belvoir, with International Harvester and Caterpillar. Successful in testing, and exciting a good deal of interest for civilian spin-off, the concept languished after a demonstration, where key decision-makers saw the vehicle sink in front of them while demonstrating its swimming ability.

The UET was originally seen as a squad vehicle, with provision for troop seats in the bowl, and was tested as a cargo vehicle, and even as a mobile mortar carrier.[2]

The M9 is a highly mobile, armored, amphibious tractor, dozer, and scraper. It was finally fielded in 1986, and is capable of supporting forces in both offensive and defensive operations. It performs critical combat engineer tasks such as digging hull defilade fighting positions for guns, tanks and other battlefield systems to increase their survivability. The ACE breaches berms, prepares anti-tank ditches, prepares combat roads, removes roadblocks and prepares access routes at water obstacles.

Two M9 ACEs staged ready to go out on a mission in Iraq.

The engine, drive train and driver's compartment are in the rear of the vehicle, while the front comprises an 8.7 cubic yard (6.7 m³) bowl, apron and dozer blade. Armor consists of welded aluminum with selected steel and aramid-laminated plates. An armored cupola containing eight vision blocks covers the driver's compartment. The vehicle hull is welded and bolted aluminum with a two speed winch capable of 25,000 pound (110 kN) line pull. Towing pintle and airbrake connections are provided. It is equipped with a suspension system which allows the front of the vehicle to be raised, lowered, or tilted to permit dozing, excavating, rough grading and ditching functions. The M9 is armored against small arms and artillery fragmentation, has smoke screening capability, and chemical-biological protection for the operator. Its roadspeed is 30 mph (50 km/h). It is transportable in C-130, C-141, and C-5 aircraft and can swim at 3 mph (5 km/h) under ideal conditions. Since the removal of swim missions as a task for the M9, the swim-related components are not required to be maintained.

By raising the dozer blade and using its scraper blade, the ACE can fill itself with ballast to improve dozing efficiency. Another key feature of the M9 is its hydropneumatic suspension system. The principal components are eight high-pressure hydraulic rotary actuators (four on each side) which connect to the roadwheel stations. During high-speed travel, this system assures a smooth ride through the use of shock-absorbing accumulators. In earthmoving operations, the operator rotates the actuators, thus lowering the apron and blade for digging.

A typical combat engineer battalion will contain 22 ACEs - seven per company plus an operational readiness float. The active Army has a total of 447 M9 ACEs.

2. Employment

The M9 performs mobility, countermobility and survivability tasks in support of light or heavy forces. Tasks include the excavation and preparation/reduction of obstacles, bridging operations, battle positions, strong points, and protective emplacements for command posts, air defense, communications equipment and critical supply/logistical bunkers. Other major tasks will be route clearing and maintenance in both defensive and offensive operations.

In Operation Desert Storm the M9 Armored Combat Earthmover (ACE) performed exceptionally well in support of combat operations. The ACE proved to be a successful combination of armored vehicle and combat earthmover that was capable of keeping pace with the manoeuvre units, while providing crew survivability. While not as efficient as the D7 Dozer in earth moving, its ability to move with maneuver forces over several hundred kilometers of desert allowed it to successfully perform a wide variety of missions such as construction of combat roads and trails, survivability positions and berms. It can not, however, move as fast as an M1 or M2. The vehicle is governed to prevent this.

But the training of ACE operators appeared to be inadequate. Operators were unfamiliar with the techniques associated with dozing, scraping, cut and fill ops, and grading. The ACE experienced trouble in reducing the berms associated with Iraqi tank ditches (berm on enemy side). Due to the location of the driver in relation to the vehicle blade, he cannot see the blade or determine when he is about to tip over. The ACE needs a front-mounted telescope or a side-mounted periscope to overcome this deficiency. The ACE led the way in breaching the border berm between Saudi Arabia and Iraq, and in reducing trench-lines during the assault breach. In both instances the ACE performed extremely well. Problems were encountered, however, due to the ACE's shortcomings. One commander referred to the ACE operator as "Alone, Unarmed, and Unafraid". This highlights the ACE's major shortcomings as a piece of mobility equipment used during direct fire engagements. ACE operators, usually 19-year-old PFC's, led the 7th Corps breach into hostile country. Fortunately, they met with very light resistance. Otherwise, mortality among ACE operators would have been very high. The ACE is a single operator vehicle,[3] without the moral and physical advantages of a crew with an NCO in charge, and without the advantage of a weapon for local suppression. Habitually, maneuver task forces provided two Bradley Fighting Vehicles to protect the ACE during breaching ops. While this is a high price to pay for protection of one vehicle, commanders deemed it necessary for the success of their operations. Commanders felt that the ACE needs an additional crewman and a protective weapon such as a .50 caliber machine gun or the Mark 19 automatic grenade launcher.

3. Basis of Issue

  • 7 per Engineer Company in a Heavy Division
  • 6 per Armored Cavalry Regiment
  • 6 per Engineer Company, Heavy Separate Brigade
  • 6 per Engineer Combat Company (Mech) Corps
  • 6 per HHC, Engineer Battalion, Light Infantry Division
  • 4 per Engineer Company, Separate Infantry Brigade (Ribbon)
  • 2 per Engineer Company (Assault Float Bridge)(Ribbon) at Corps
  • 1 per Engineer Company (Medium Girder Bridge)
  • 1 per Bridge Company (Ribbon)

4. Training/Personnel

TRADOC instructors and New Equipment Training Teams (NETT) will be trained by the contractor. Initial training will be by NETT for Combat Engineer organizations issued the M9. Institutional training at U.S. Army Engineer Center at Fort Leonard Wood will provide training for the operator (MOS 12F) and maintainer (MOS 91L). Operator proficiency will be maintained by Training Extension Course tapes and extension training materials.


  1. Jane's Defence Weekly 5: 269. 1986. 
  2. [universal Engineer Tractor "Do-everything tractor can be dropped from sky"]. Popular Science 181 (4): 110–111. October 1962. universal Engineer Tractor. 
  3. M9 Armored Combat Earthmover
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