M9 Armored Combat Earthmover

The three primary missions of the Engineers in combat are mobility, counter-mobility, and force protection. Rather obviously, this means ensuring our freedom of maneuver, by improving roads and reducing obstacles, both natural and man made; emplacing obstacles to slow, channel or turn an enemy force; and digging or building positions for friendly forces.

As you might expect, a large portion of this can be accomplished by earthmoving. As a mechanized Infantryman mounted on a Bradley, my most common interaction with the Engineers was when we had a D7 bulldozer dig fighting positions for our vehicles.

Merely pushing a berm in front of the position does little to offer protection for fighting vehicles. While it might defeat HEAT rounds, kinetic rounds hardly notice a dirt berm before passing through the frontal armor, engine block, turret basket and troop compartment and then exiting the rear ramp armor. So the position is dug deep enough to fully conceal the vehicle. But the vehicle also has to be able to fight from the position, so there is a step on the front half of the position that the Bradley can drip up on, exposing only the turret, giving it a field of fire. Pop up, shoot, scoot back, scan for the next target. In gunnery terms, this is known as a “berm drill.”

While the D7 bulldozer is very, very well suited for digging said positions, it is not without its drawbacks.


First, it is completely unarmored. If the position isn’t completely secure, the operator is at an unacceptable risk. But failing to construct the positions then places the fighting vehicles at a completely unacceptable risk.

Secondly, the D7 is rather slow, with a maximum speed of around 7 miles per hour. That means it has to be transported from location to location on a heavy equipment trailer. That also means the trailer is restricted to relatively good terrain. The truck and trailer also are unarmored, and add an additional logistical, manning, and maintenance burden.

And so, starting in the late 1980s, the Army began fielding a lightweight vehicle known as the M9 ACE or Armored Combat Earthmover. A relatively lightweight tracked vehicle with a bulldozer blade on front, it was proof against small arms fire and artillery fragments. The driver was protected. The hydropnuematic suspension allowed it to travel cross country, and on roads at a respectable 30 miles per hour or so. Maybe not enough to keep up with Bradley’s and M1 Abrams, but enough that the wait for ACE shouldn’t be too long.

Light weight is a disadvantage for a bulldozer, though. The tracks need significant weight on them to increase the dozing ability. So the M9 can actually also act as a grader/scraper, and load a ballast compartment just behind the blade with earth to improve its earthmoving ability. When it is done, it can also eject that earth. In between missions, that space can be used to carry cargo or engineer supplies.

[youtube https://www.youtube.com/watch?v=ziRFkFW9upE]

My experience with the M9 is very limited. I have heard that some dozer operators didn’t like it, and felt it was a rather poor earthmover, especially those who had previous experience with the D7. It has also had a long, long history of maintenance issues, primarily associated with its complex suspension system.

What’s especially interesting is the long development time of the M9. As I mentioned, the Army didn’t start buying the M9 until the late 1980s. But that doesn’t mean it was a new design. Its design actually dates back to the early 1960s.

[youtube https://www.youtube.com/watch?v=BTXOg2OZLEQ]

With a few minor changes, the UET would become the M9. So why the 20 year gap between design and fielding? First, just as the Army was finishing development, Vietnam happened. And the money that would have gone for the UET instead went to fighting that war. In the years after Vietnam, the Army’s funding priorities were on the Big Five, the M1, M2/M3, UH-60, AH-64, and Patriot missile. It wasn’t until those programs were well in hand that other priorities could be addressed.

11 thoughts on “M9 Armored Combat Earthmover”

  1. ACEs are a maintenance nightmare. They fail quickly, require unique POL, and are much slower to dig in a tank than is a D7, primarily due to the narrow blade. Give me D7s. By the way, digging in is, like everything else, a lost art. I brought some dozers out to dig some real two-tier fighting positions for my platoons to practice with, and wound up having to advise the operators from the engineer battalion, who had never dug one before.

  2. As a guy who had an ACE squad in his platoon 15 years ago, they’re decent vehicles. You point out the disadvantages of the D7 pretty well. That said the D7 once it shows up can do a helluva lot of work. Rough rule of thumb – 1 D7 = 1 team of 2 ACEs (maybe a bit faster, depending on terrain- with the D7 having even more of an advantage in rocky harder terrain). Digging with an ACE also takes a lot of skill, and you’re assigned mostly E1s-E4s there, so nobody with more than a couple years experience at best- and most don’t last more than a year.

    There’s miles of hydraulic lines and actuators in the ACE (primarily because you have to tilt the whole vehicle to adjust the blade while digging – so the whole ACE tilts like one of those rap video cars), any of which is just waiting to burst. That said- with a good squad leader and regular exercise at home station (meaning taking them out and digging regularly- ensures that anything that’s about to go goes and gets fixed and also ensures that the seals stay wet and don’t try out), they can be good vehicles (didn’t say great or perfect). I will say that my ACE squad when we deployed with our armor battalion had a better OR rate than the M1s we were attached to.

    The D7s probably come from a Combat (Heavy) battalion or Combat Support Equipment (CSE) Battalion – more likely trained to make roads or foundations for buildings so, yeah they’re going to need supervision to make a good position for you.

    1. True, these D7s came from a support ENG unit and were reorganized into the newly-formed Brigade Engineer Battalion, which thankfully gets D7s. Having been supported by both in the old days, I will take the D7s any day, though I am okay with M9s digging in the Brads; just not the tanks. Good point witht the skill level of the operators.

  3. The Battalions of the 30th Armored BDE, when I was in, had Tank Dozers. Not as good as the D-7, but a better substituted than the ACE. This was ’85-’87.

  4. Re: Esli,
    I reread my reply – I should point out that having a better OR rate than the M1s we supported was a result of a lot of hard work by the squad leader and troops and was not a regular occurrence by any stretch. With respect to operator skill level, I had one guy who was a natural- I’d put him up against a 2 ACE team and I’d bet he’d beat just about anybody. Don’t know if I’d bet on him vs. a Dozer 🙂 The ACEs did fine on loose soil (like we got in the dig areas around Ft Lewis). My memory tells me they did a lot worse out in Yakima where the ground is a lot more rocky as you go down.

    I think they would have been better if commanders didn’t baby them so. Let the thing do what it’s supposed to- if something breaks fix it. But it had a reputation and a lot of visibility so I think there was a lot of pressure on the engineer company commanders to get them FMC and then don’t touch them for fear of breaking them. I was lucky enough to have a commander who listened to my squad leader (through me) and let us do what we thought was right.

    Overall it’s a tradeoff and a mix of both ACEs and Dozers is probably a good thing. I wouldn’t want to be the guy that has to fill in an antitank ditch in an unarmored D7 or scratch out a fighting position while under the threat of indirect fire. By the same token, digging through solid rock in an ACE ain’t going to happen without a lot of heartache.

    1. Well said. Though I will match my Abrams’ OR rates against anyone! I did get some cool video of my tank doing berm drills last time I took it out. Wish I could post them here. I owe our host some other video too, and don’t want him to start nagging me over it.

  5. If I recollect accurately the IDF uses a Caterpillar variant that they (IDF) up armor the heck out of for digging in, and bulldozing the homes of suicide bombers and/or their relatives.

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