To put it simply, the Armoured Combat Earthmover M9, often just known as ACE, is a battlefield bulldozer. The vehicle is intended as a highly mobile, protected earth moving vehicle for combat engineers. It is a valuable support vehicle to armored, mechanized and infantry units. In combat operations, the M9 ACE can perform a number of tasks in support of friendly units. These include mobility (clearing a safe passage of blockages), counter-mobility (route-denial, the reverse of mobility tasks), and survivability tasks (constructing defensive positions). The M9 features a number of innovative features, such as a hydropneumatic suspension, a ballastable front end, and the ability to be amphibious.
The first vehicles entered service 1986, with the vehicle serving in most major operations with the United States Military ever since, most notably in The Gulf War (1990-1991) and The War in Iraq (2003-2011).
Despite all of their uses and features, the M9s were highly unreliable and, as such, loathed by the troops it was there to support. Hydraulic and mechanical failures have plagued the ACE throughout its service life. To try and salvage the tattered reputation of the vehicle, an extensive upgrade program began in 2014, and, for now at least, these upgrades keep the M9 in service.
Badge of the M9 ACE. Photo: MAS
A search for a battlefield engineering vehicle that was capable of earthmoving tasks had been sought after since the mid-1950s. Initially, this led to the development of a vehicle known as the All-Purpose Ballastable Crawler, or ‘ABC’, that was developed in 1958. This nomenclature was later changed to Universal Engineering Tractor, or ‘UET’. One of the features of the UET was that it could also carry troops in the empty ballast bowl via fold-out seats. This feature was later dropped, however.
What would go on to become the M9 appeared in 1977. The Engineer Laboratory at Fort Belvoir, Virginia, with added assistance from the International Harvester Co. and Caterpillar Inc., was responsible for the initial development of the vehicle. Pacific Car and Foundry were given a contract to build no less than 15 prototypes, based on the cumulative design of the three co-developers. These were completed by the early 1980s. After some additional improvements to the design, a contract for full production was signed with Bowen-McLaughlin York (BMY, now owned by BAE Systems). In total, 566 vehicles were ordered to be built. Due to budget cutbacks, however, only 448 of the vehicles were acquired. The first vehicles entered service in 1986, with production running into 1991.
The prototype Universal Engineering Tractor (UET) demonstrates its digging capabilities. It is unknown where or when the photo was taken, but the location is likely that of the BMY proving grounds. Photo: Wisconsin History
General Specifications & Features
The M9 is not your every day 50 ton/tonne, earth-scraping, lumbering brute of a bulldozer. In fact, it is the exact opposite. The ACE is lightweight at around 16 tons (16.3 tonnes), allowing it to be highly mobile. This light weight is partly due to its welded and bolted steel and aluminum construction. The M9 is 20 feet 6 inches (6.25 m) long, 10 feet 5 inches (3.2 m) wide, and 9 feet 6 inches (2.9 m) high. The ACE’s lightness and compact size allow it to be air transportable by C-130 Hercules, C-141 Starlifter, C-5 Galaxy or C-17 Globemaster cargo aircraft. It also allows it to be amphibious. In ideal conditions, the vehicle can travel in water at 3 mph (5 km/h) using the rotation of the tracks to propel it. This was a feature that mostly went unused and consequently, most vehicles have had the amphibious equipment removed or it has simply gone unmaintained.
Early production model of the M9 ACE. Photo: Presidio Press, Sheridan
Only the rear-most portion of the vehicle is armored. This consists of welded aluminum with selected steel and aramid-laminated plates. This armor is in place to protect the single operator. It is intended to protect him against small arms fire, shell shrapnel, or a mine detonation. It is no match for a tank shell or missile though. The operator is located at the rear left of the M9 under an armored cupola with eight vision blocks. When operating head-out, a small windscreen with integrated wiper can be folded up to protect him from dust and debris. In combat conditions, however, the vehicle is operated with all hatches closed. Due to the location of the position, visibility was extremely poor, as the Operator could not see the ground directly in front of him. The M9 also has an optional NBC (Nuclear, Biological, Chemical) protection system. The Operator enters the vehicle through a cut out at the back of the M9 that doubles as a channel for the radiator to vent out through. Once he has climbed into this channel, the operator can turn left and climb in through the cupola’s hatch.
A side on view of the M9 showing its unique profile. Note the individual armor panels on the side of the hull, protecting the Operator’s position. Photo: Sabot Publications
Quite clearly, the most important feature of the ACE is its ability to move earth. This is achieved with the use of an 8.7 cubic yard (6.7 m³) blade at the front of the vehicle. The lower half of this blade, which is also known as an ‘apron’, can fold upwards for road marches and travel and is held in place via sprung latches. The blade allows the M9 to carve out hull-down positions for gun tanks, dig gun emplacements, perform route denial (creating and filling anti-tank ditches), and improving bridge approaches. It could also be used aggressively to push barricades or debris from the path of attacking allies. If needed, ‘ripper’ teeth can be bolted into the lip of the blade.
Someone familiar with the operation of bulldozers may query how such a light vehicle can be an effective earthmoving vehicle. This is where the ballastable aspect of the M9s design comes into play. Behind the apron is a large ‘bowl’, an empty space designed to hold ballast to increase the vehicle’s weight. To fill this ‘bowl’, the dozer blade is lifted via hydraulic rams. The vehicle is then driven forward, gathering material in the void. At the front of the ‘bowl’, there is a small ‘scraper’ blade on the bottom lip, making shoveling easier. The vehicle will then back off and the dozer blade ‘apron’ lowered to cover the opening. With the added ballast, the M9s weight increases by up to 8 tons/tonnes, bringing it to 24.1 tons (24.4 tonnes). The added weight allows the ACE to shift larger and heavier amounts of material without much extra effort.
An M9 ACE in a training environment fills its ballast bowl with ‘apron’ lifted. Photo: Sabot Publications
The added ballast also gives the ACE equal pushing/towing strength to the Caterpillar D7, a commercial bulldozer twice the weight of the M9 (that also served in the US Military), thanks to the increased tractive effort applied by the added weight. To discard the spoil, there is a hydraulic ram propelled blade that pushes the spoil out of the bowl. The blade is guided by two supports with casters attached, these casters run in a channel and keep the blade straight. When empty, the ballast bowl can also be used to carry small loads of cargo. The vehicles head lights are placed directly on top of the ‘apron’.
2 views of the ACE. On the left, A photo looking down into the empty ballast bowl of the M9. The internal blade is clearly visible and pushed all the way forwards behind the ‘apron’. On the right, a view of the dozer blade with the lower-half folded for travel. Photos: Sabot Publications
The M9’s power plant and transmission are located at the very back of the vehicle. The engine, an 8-cylinder Cummins V903C diesel, is rated at 295hp and can propel the vehicle to a top speed of 30mph (48 km/h). This top speed allows the vehicle to keep up with tanks and other armored vehicles in convoys, and allows for rapid deployment.
The M9 features a hydropneumatic suspension. There are four road wheels per side, each one connected to a high-pressure hydraulic rotary actuator. Instead of rubber, which can crack or shed chunks, the wheels are surrounded by a high-tensile polyurethane (plastic) tire. The drive sprocket is mounted at the rear, slightly higher than the road wheels. There are no idler wheels. The hydropneumatic suspension is a necessary feature as, because of the ballast bowl, the dozer blade could not be lowered to meet the ground. The suspension has two modes; Sprung and Unsprung. Sprung mode is engaged for travel and allows the vehicle to travel at top speed and traverse rough terrain and minor obstacles as the suspension arms can travel to their maximum degree. Unsprung mode almost flattens the suspension and limits the travel of the suspension arms, thus tipping the vehicle forwards so the blade or mouth of the ballast bowl can meet the ground.
Diagram showing the different suspension modes. Photo: Presidio Press, Sheridan.
The M9 is completely unarmed, aside from any personal weapons the operator might carry. For defensive purposes, the ACE is equipped with eight smoke grenade launchers. These are located in two four-tube banks at the center of the M9, just behind the ballast bowl. These can also be used to provide a smokescreen for allies.
At the rear of the M9 is a two-speed winch capable of a 25,000 pound (110 kN) line pull. This can be used to rescue allied vehicles or pull itself out of a ditch (even one of its own making) if necessary. The M9 is also equipped with a towing hitch at the rear, mounted just above the winch. This can be used to tow supply trailers and other equipment. Using the hitch, the M9 has a drawbar pull of 31,000 pounds (14,074 kg) at a speed of 1.5 mph (2.4 km/h).
M9 Operator, Sergeant Chad Post, 9th Engineer Battalion, sat in the passageway at the rear of the M9 after a mission. Note the winch at the very bottom of the vehicle and the tow hitch just above it. Sgt. Post was a rare example of a man who enjoyed operating the M9. His friend, Andrew Patton, said he was “…the best ACE operator I ever met. This dude would have married one and taken it home if they would have let him…” Photo: Specialist Andrew Patton, 9th Engineer Battalion
Thanks to the hitch, the M9 is sometimes used to tow the M58 Mine Clearing Line Charge or ‘MICLIC’. These devices are used to clear large areas of explosive devices or blast a path through obstacles by use of a rocket that tows a line of explosives. The M58 is placed in a large armored crate located on a simple two-wheeled trailer. The line is 350 feet (107 meters) long and contains 5 pounds (2.2 kg) per foot (30 cm) of C-4 explosives. A total of 1,750 pounds (790 kg) per line. The MICLIC is fired forwards over the vehicle, and if it fails to detonate electrically, it can be manually triggered by time-delay fuses along the length of the line. The line is attached to the rocket via a nylon rope and can reach a distance of 100 – 150 yards (91 – 137 meters). To put this into perspective, an American Football pitch is 100 yards long. When detonated, the charge can clear a lane 110 yards (100 meters) long, and 9 yards (8 meters) wide. This device is often towed, but two of them can be mounted directly to the Assault Breacher Vehicle (ABV).
M9 ACE towing the M58 ‘MICLIC’. This ACE also has the the optional ‘ripper’ teeth installed on the blade. Photo: Public Domain
A later addition to the M9, made with its operation in hot countries such as Iraq, was a cooling system for the Operator. One of the problems with the ACE was that the operating cab was right next to the engine, meaning the compartment would often get unbearably hot. This is not ideal in a desert climate. The cooling system took the form of a vest known as the Microclimate Cooling System or ‘MCS’, designed by Cobham. The vest is filled with a water-glycol mix and is powered by a control unit. In the case of the M9, this was placed in the entry passageway.
This was a much-needed improvement to the comfort of the operator. However, it didn’t always go right, as this light-hearted account by Specialist Andrew Patton, 9th Engineer Battalion demonstrates:
“I remember watching a friend, a guy called Nate, use it for the first time. We went out on a mission to build up a berm around an Iraqi Police station. The ACE operator worked hard for a few hours and then when his part of the mission was done he parked his ACE, closed the hatch and took a nap with the vest on but the engine off. Half an hour later the dude threw open the hatch, jumped out, threw his body armor to the ground, shed the cooling vest and stood there shivering in the 110-degree heat…apparently without the engine to heat up the compartment he actually managed to get too cold wearing the thing…”
The Microclimate Cooling System by Cobham. Photo: Cobham plc.
The Armored Combat Earthmover M9 ‘ACE’. It is featured here a Desert paint scheme, as it did in Iraq and Afghanistan.
The newer model of M9 ACE in an Olive Drab paint scheme. The hydraulics are activated with dozer blade in scraping position.
Both illustrations are by Ardhya Anargha, funded by our Patron DeadlyDilemma through our Patreon campaign.
Typically, the ACE is distributed with 22 vehicles per Engineer Battalion, equating to seven per company including an ‘Operational Readiness Float’ (all necessary equipment). Almost all of the 448 production vehicles are in service with the US Army. The United States Marine Corps (USMC) has 100 M9s in their arsenal.
Two M9s of the 43rd Combat Engineer Company, 3rd Squadron, 3rd Armoured Cavalry Regiment work together to clear the highways of Mosul. The M9 on the right is using its blade to fill the ballast bowl of the left M9 with debris so it can be taken away. Note the roughly added armor panels over the Operator’s position on both vehicles. Photo: Sabot Publications.
A number of faults have plagued the ACE throughout its service life. Multiple mechanical failures, mostly caused by the hydraulics, have given it a highly unreliable reputation. Even with its mobility and weight-gaining features, the M9 has become viewed as useless by many troops that served with them or has simply required the use of one. The general feeling of many was: “We’d rather have the CAT”, referring to the old reliable Caterpillar D7. Even the M728 Combat Engineering Vehicle (CEV) with its attached dozer blade was a preferred choice, at least up until its retirement in the mid-to-late 1990s. The quote below displays that feeling exactly:
“Hated when one showed up to dig my battle position, they were horrible and very unreliable. Hydraulic system always breaking. Loved me the D7 CAT our engineers used. They did use them [the M9] on occasion to transport EPW’s in ‘03, so I guess they did have some use.”
Joe Daneri, US Army, retired.
The M9 is issued in the following order:
Engineer Companies in a Heavy Divisions: 7
Armored Cavalry Regiments: 6
Engineer Companies, Heavy Separate Brigades: 6
Engineer Combat Company (Mech) Corps: 6
Headquarters and Headquarters Company (HHC),
Engineer Battalions, Light Infantry Divisions: 6
Engineer Companies, Separate Infantry Brigades (Ribbon): 4
Engineer Companies (Assault Float Bridges)(Ribbon) at Corps: 2
Engineer Companies (Medium Girder Bridge): 1
Bridge Companies (Ribbon): 1
The M9 ACE has served in the Gulf War (1990-1991), the Bosnian War (1992-1995), the Kosovo War (1998-99), the War in Iraq (2003-2011) and the War in Afghanistan (ongoing). Unfortunately, the only real records of the M9s operation in a combat zone come from the Gulf War and the War in Iraq. Even then, they are sparse details at best. None the less, what is known is presented in the following sections.
Gulf War (1990-1991)
Operation Desert Storm, the combat phase of the Gulf War, is where the M9 ACE saw the most action, performing well in combat operations. It proved highly effective as Coalition forces assaulted Iraqi units in the besieged Kuwait City. They rolled through roadblocks and smashed through Iraqi fortifications in breaching operations. Despite having a similar pushing/towing strength as the D7 Caterpillar, it was soon found that the M9 was not quite as efficient when it came to earthmoving. However, its flexibility and maneuverability were appreciated by mobile armored units, especially when traversing vast swathes of desert. This somewhat made up for the slightly less effective digging ability. The armor on the M9, though thin, was still far better than the D7, a feature appreciated by the operators.
An ACE of the 5th Marine Regiment, tows a ‘MICLIC’ trailer across the desert in Kuwait. Photo: Lance-Corporal Andrew P. Roufs
ACEs led the way when American Forces breached the border obstacles between Saudi Arabia and Iraq, demolishing trench lines along the way. However, the reliability issues of ACE and its general shortcomings did cause problems and a number of delays. When the M9 suffered a hydraulic fault, it could take many hours, or even days if more than one went down (not a rare occurrence) to repair.
The War in Iraq (2003 – 2011)
The poor reputation of the M9 was set in concrete by the start of the Iraq War in 2003. A number did serve in the 8-year conflict, much to the chagrin of many an American soldier. By the later stages of the war, its flaws were plainly clear. It became apparent that the ACE had trouble dismantling enemy anti-tank obstacles such as berms or ditches. Due to the location of the operator in relation to the blade, he cannot see the ground he is scraping resulting in the risk, when tackling a ditch, of toppling forwards into the void.
“When digging a battle position for a Tank, they were useless in my opinion. I always preferred the CAT dozers, especially when you hit rocky subsurface. Just hope they had their rippers installed. Even the M88 was more useful than an ACE when back blading the spoil. If our mechanics weren’t busy they’d help out in some units.”
Joe Daneri, US Army, retired.
An M9 ACE is used to scrape a road clear in Iraq. Photo: 20th Egineers
Second to this, the lack of armor in a War full of IEDs (Improvised Explosive Devices) and RPG (Rocket Propelled Grenades) wielding insurgents began to trouble many Operators. One officer described the M9 Operator as: “Alone, Unarmed, and Unafraid”. This flaw was amended somewhat, but in a manner that didn’t make many other units happy. It became standard operation for two M2 Bradley IFVs (Infantry Fighting Vehicles) to protect the M9 as it went about its business. That is two vehicles, intended to support infantry, occupied with the protection of one vehicle, leaving infantry units without armored support. It was deemed necessary for operation success, however, as the M9 could not defend itself as it was completely unarmed.
In early-2007, a couple of famous M9s took part in an operation in Ramadi, a city in central Iraq. The aim of the operation was to install an Observation Post (OP) between Camp Ramadi and a Combat Outpost called ‘Steel’. The M9s in question were ‘Dirt Diggler’ and ‘The Quicker Pickerupper’/’Bounty’, belonging to C. Company 9th Engineer Battalion, 1st Infantry Division.
The M9s in question. ‘Dirt Diggler’ and ‘The Quicker Pickerupper’/’Bounty’ post operation. Photo: Specialist Andrew Patton, 9th Engineer Battalion
Both of these M9s have quite a story regarding their names…
“After having waited quite some time for the order to move out a bored and rebellious M9 ACE operator named Nate* pulled out a can of spray paint and shocked everybody by graffitiing his vehicle with the now famous “Dirt Diggler” name. The second ACE operator followed suit and painted his vehicle to say “The Quicker Picker Upper, Bounty”. Upon seeing the graffiti, our chain of command nearly lost its collective minds, because spray painting a military vehicle isn’t received much better than graffitiing a building. I stood at a distance and watched as everybody in Nate’s chain of command took turns exploding at him with shocked rage at what he had done. He later told me that our First Sergeant had among other things, threatened that if the paint was still there after the mission, Nate would be removing it with a toothbrush. Naturally, as a lower enlisted man, I thought this was all very funny and made a point of taking several pictures to preserve the incident…luckily for the two M9 ACE operators the spray paint rubbed off almost the instant the dozer blade touched the dirt. No one was punished for the graffiti and the rest of the company’s ACE operators took notice of this and it became a bit of a tradition of ours to graffiti the dozer blade prior to each mission…”
– Sample of a written account by Specialist Andrew Patton, 9th Engineer Battalion. Used with permission.
*This is the same Nate involved in the MCS incident
A few M9s also took part in Operation Thunder Reaper, a route clearance operation which took part in December 2007 in Mosul. The objective was to clear the major highways so they once more became usable by civilians. This consisted of scraping the roads clear with the M9s followed combat engineers repaving them where necessary. The Operation resulted in the clearance of around 10 miles (15 kilometers) of highway.
In 2014, an upgrade program that had been running for almost eight years ended. It aimed at fixing the multiple problems that made the M9 such a hated vehicle. These feelings are echoed in the quote below from Joe Klocek, the product manager for Engineer Systems at U.S. Marine Corps Systems Command, Quantico.
“There were performance issues and reliability issues that were becoming a major problem, the initial system was fielded before Operation Desert Storm, so we were dealing with some ‘70s technology.”
The ‘1970s technology’ referred to was the intricate, hard-piped hydraulic lines which so often malfunctioned resulting in lengthy periods in repair shops inactive. It also included the lever-based control systems that made precise work difficult. Visibility was another major issue with the M9, as in combat conditions, the Operator had to control the vehicle ‘buttoned up’ (all hatches closed). To quote, Klocek: “Imagine trying to punch through an anti-tank ditch, 12 feet deep and eight feet wide, and not being able to see anything.”
The visibility problems were solved by the introduction of a 360-degree camera system (consisting of 10 separate cameras) by Leonardo DRS called the Vision Enhancement System (VES). No longer is the operator blind to what’s happening directly in front of the dozer blade. The system also provides night vision.
The hydraulic levers were replaced with joysticks, allowing for vastly improved and precise control. This was accompanied by a redesign of the highly problematic hydraulic subsystems. A new, more powerful engine was also added, but the specifics of this are currently unknown. This allows it to be more effective in its bulldozing role. Other improvements include an automated track-tensioning system, improved hull construction, automated fire extinguishers, and a redesign of the internal electronics.
The upgrade M9 ACE was unvieled and tested in 2014. Photo: defense media network
It remains to be seen whether the new upgrades to the M9 ACE will repair its tattered reputation, and prove itself useful to the Modern US Military.
There were other upgrade options for the M9, such as a possible remote control version using a ‘Standard Robotic System’ (SRS) by Omnitech Robotics of Colorado (as used on the M1 Panther II) but, for unknown reasons, this was not accepted. New vehicles that fulfill similar roles as the M9, such as the M105 DEUCE (DEployable Universal Combat Earthmover), also started to appear in the early 2000s, putting pressure on the M9 ACE to perform.
For now at least, the upgrades the M9 has received keep in service with the US Military for the foreseeable future. The vehicle is also currently in service with the Taiwanese and South Korean Military.
An M9 ACE on display at the Army Proving Ground’s (APG) 100-year anniversary show in May of 2017. Photo: Richard S. Eshleman.
|Dimensions (L-w-H)||20′ 6” (6.25 m) x 10′ 5” (3.2 m) x 9′ 6” (2.9 m)|
|Total weight, battle ready||16 tons (no ballast), 24 tons (full ballast)|
|Propulsion||Cummins V903C, 8-cylinder, diesel|
|Maximum speed||30 mph (48 km/h) on road|
Discussion with Andrew Patton, former Specialist, 9th Engineer Battalion, Iraq War veteran. A written account of some of his expieriences with the M9 can be found HERE.
Presidio Press, Sheridan: A History of the American Light Tank, Volume 2, R.P. Hunnicutt
Sabot Publications, M9 ACE: Armored Combat Earthmover, Chris Mrosko & Brett Avants
Armoured Vehicle Database
Military Analysis Network (Future Upgrade details)
M9 ACE Armored Combat Earthmover In Detail
The M9 ACE in Detail is a 132 page full color photo journal of the U.S. Army’s armored combat earthmover. The book contains extensive color photos of the ACE in action in the field, and a comprehensive walkaround section for the detail-oriented. Makes a great companion to the Takom 1/35 ACE model kit!