This compact tank, officially known in U.S service as the Light Tank M5A1, is a World War 2 veteran. It’s also a Cadillac: If you remove its rear engine covers, you’ll find two 1940s-vintage Cadillac flathead V-8 engines and a pair of early GM four-speed Hydra-Matic transmissions. No, it’s not some weird custom job — Cadillac built thousands of these speedy little tanks between 1942 and 1944, a couple of which were parked next to a gas station in West L.A.
The Bring a Trailer listing for this tank finally answered a question I’d been wondering about for a long time. These photos were all shot (not by me) just a few blocks from my apartment, next to a gas station and car wash down the street. Since 2016, there has been a succession of old tanks parked there, including a couple of WW2 light tanks (which for a while I thought might be the same tank in various stages of restoration) and later a Korean War vintage M41 Walker Bulldog. They were obviously collector’s pieces, but no one could tell me whose, or why they were parked at a gas station next to the freeway. It turns out they were WOB Cars dealer consignments, awaiting auction: The one pictured above sold for $330,000 in November 2025.
I’m also mixing in photos of another M5A1 offered by the same seller, which was ALSO parked at that same gas station for a while (and was photographed in the same spot); this tank sold for $220,000 in May 2018.
Having seen the M5A1 close up, I can tell you that this is a little tank. Including its rear stowage box, the M5A1 was 190.5 inches long, which was a bit shorter than a late ’60s Dodge Dart, although at 90 inches wide, it was about 10 inches wider than a ’70s Lincoln. Its 42-foot turning circle was actually smaller than most Cadillac sedans’! With a four-person crew, fuel, and ammunition, the M5A1 had a gross weight of just under 34,000 lb.
The M5 was, literally, the Cadillac of light tanks. Cadillac built 5,000 M5 and M5A1 tanks, 56 percent of production; another 1,550 were built by GM South Gate Assembly plant here in Los Angeles, with a total of 2,334 more built by either Massey-Harris in Racine, Wisconsin, or American Car & Foundry in Berwick, Pennsylvania.
All had Cadillac engines, which were very similar to the ones used in Cadillac production cars of the early 1940s, and all used a variation of the Cadillac version of GM’s Hydra-Matic transmission, which Cadillac had only started offering on its production cars a few months before this tank was developed.
Originally called the M3E2, the M5 was conceived in the spring of 1941 as an adaptation of the existing M3 Stuart light tank, which the U.S. was supplying in large numbers to the British under the Lend-Lease Act. Demand for the Stuart’s air-cooled seven-cylinder Continental radial engine was outstripping production capacity, so Cadillac proposed an alternative powertrain using two Cadillac engines, driving a common transfer unit. This was eventually combined with redesigned armor and some other improvements, and went into production in April 1942 as the Light Tank M5. It was superseded in November 1942 by the improved M5A1, which was built through June 1944. Total production of both versions was 8,884, with the M5A1 accounting for about three-fourths of that total.
In the M5 and M5A1, the Cadillac engines were mounted in the rear of the tank, with their fans facing towards the rear.
Each engine had its own automatic transmission, bolted to the engine flywheel in the usual fashion, driving a short propeller shaft with U-joints at each end.
The radiators were mounted horizontally above the engines. Each carburetor drew intake air through a long pipe from a gigantic air bath air cleaner at each rear corner of the tank.
The carburetor throttle linkages for the two engines were linked by a horizontal cross shaft, operated by a series of mechanical relays from the accelerator pedals at the front of the tank.
Each engine was a 346-cid L-head “monobloc” V-8. Except for their 12-volt electrical systems, these engines were basically the same V-8s found in 1941–1942 Cadillac passenger cars, rated at 150 gross horsepower or 110 hp net. They retained hydraulic lifters, and the two-carrel Carter carburetors even retained their standard automatic chokes.
The transmissions were mostly stock Cadillac Hydra-Matic transmissions, with a fluid coupling and four forward speeds. Their main departure from normal Cadillac passenger car specification was that they lacked the reverse gearset and had oil-to-water transmission oil coolers; most early passenger car Hydra-Matic transmissions were air-cooled and a third planetary gearset for reverse.
Each engine was angled so that the two transmission propeller shafts formed a “V,” coming together at the back of the transfer unit.
The transfer unit combined the power of the two transmissions, but it was also essentially a second two-speed automatic transmission in its own right. It would shift automatically between direct drive and a 2.37 reduction gear based on road speed and throttle position, just like the Hydra-Matic transmission. It also provided reverse gear.
Combined with the transmission gears, the transfer case gave a total of six forward speeds. (The transfer case reduction gear couldn’t be used in all transmission gears, although the ratios would have overlapped too much to be useful anyway.) Ahead of the transfer unit were the differential, which had a 2.62 ratio, and the final drive that operated the drive sprockets for the treads, which had an additional 2.57 ratio. When starting from rest, there was a total reduction of 51.9 to 1 to get this 17-ton tank moving.
In both the M5 and M5A1, the driver sat in the left-hand seat. The right-hand seat was for the co-driver/bow gunner (which the U.S. Army called the “BOG”), who had a backup set of driving controls (though no instruments) in case the driver was hit. The gunner and commander were both in the turret behind them.
The driver’s instrument panel (which was revised several times in production) had a single speedometer, two tachometers, two sets of coolant temperature and oil pressure gauges, and a single ammeter. There was a control for the hand throttle at the top of the panel and ignition and starter switches at the bottom.
To start a tank like this, you first pulled both steering levers all the way back, which locked the parking brake. You then pressed the accelerator not quite halfway, moved the transmission selector to N, turned on the ignition switch for each engine, and pressed the starter buttons. Once the engines were running, you used the handle throttle to set the idle speed and gave the engines a few minutes to warm up to normal operating temperature and circulate oil through the drivetrain before setting out.
The above video shows one of these M5A1 tanks being driven in a parking lot next to the gas station. You put the tank into motion by releasing the hand throttle, moving both the transmission and transfer unit selectors to “DR,” pushing the steering levers forward far enough to release the parking brake, and then pressing the accelerator. These tanks used differential steering, so the hand levers served for both steering and braking: Pulling the right lever back caused the tank to turn right, pulling the left lever caused it to turn left, and pulling both levers applied the brakes to bring the tank to a halt.
The transmission and transfer case shift levers were to the right of the driver’s seat. The transmission used the standard Hydra-Matic NDLR shift pattern, but with an added reverse lockout.
Both the transmission and transfer case also had manual LO ranges for ascending or descending steep hills at low speeds (below about 12 mph). Otherwise, you could just leave the powertrain to shift for itself. There was even a kickdown detent downshift for quicker acceleration or climbing grades, just like in a car.
Obviously, driver visibility was not a strong point. In hot weather, both front seats could be raised high enough to let the driver and co-driver ride with their heads sticking out of the top hatches, although in that case, the driver couldn’t see the instruments. Each hatch also incorporated a rotating periscope that could be used when buttoned up, and the driver and BOG could each open a tiny viewing port in the front armor, normally covered by a steel plug. Either way, parallel parking was not advised.
With 17 tons to haul, the M5A1 wasn’t going to win any drag races, but it could climb a 60 percent grade and had an official top speed of 36 mph, which was pretty fast for a tank of that era. Speed was important because the M5 and M5A1 had very thin armor, even in front. They were also lightly armed, with a 37mm main gun and three light machine guns; light tanks like this were used mainly for scouting rather than slugfests.
Official range of the M5A1 was 100 miles, but cautious driving on straight improved roads might eke out up to 172 miles — about 2 mpg.
If you’re inclined to claustrophobia, you might be concerned about how one gets out of this thing. This Cadillac tank was technically a four-door: The driver and BOG could get in and out through the hatches over their heads, and there were two more doors in the back of the turret. The M5A1 also added an escape hatch in the floor behind the BOG’s seat.
I had been wondering for a long time about the vertical widgets on the outside of the turret (which seemed to fascinate the photographers a lot more than some more important functional components, like the engines or transmission controls). I learned that those widgets are called “grousers,” which are to tracked vehicles what tire chains are to cars: When confronted with snow, sand, or loose dirt, the crew could remove the grousers from the turret and attach them to the tracks for extra grip.
Although the War Department had been wary of using the Hydra-Matic transmission, fearing it would be too complex, both the engines and the transmissions on these tanks worked out quite well. Cadillac subsequently used a similar powertrain in the long-serving M24 Chaffee, which replaced the M5A1 in 1944. The biggest mechanical problems with the M5 were actually with the automatic transfer case, which was replaced on the M24 with a manually operated two-speed transfer unit.
As a weapon, the M5/M5A1 was more or less obsolete by the time it started rolling off assembly lines. As a vehicle, it was reasonably reliable, fairly easy to drive (visibility problems notwithstanding), and about as civilized as this kind of vehicle got — just as you’d expect of a tank made by Cadillac.
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Nice, in-depth article. From what I’ve read the Cadillac/TH combo worked very well and had no reliability issues. Crews much preferred it over the earlier Continental radial engine models as they used high octane AV gas which was much more flammable.
The controls on the M-113 APCs we drove in Korea in the mid-80s were essentially the same as the M5.
There’s a funny catch with the later M24 Chaffee actually !
Its transfer case was two speed AND reverse (also fully synchromeshed, the luxury), and the transmissions were not identical to the M5’s, but rather special units with no reverse, so that the end bearing was contained within the length of the transmission body and the output end of the transmission was a flat-ish face rather than a traditional tailhousing.
This was done so you could shorten the transmissions, have the transfer case right behind them (well, in front actually, when looking at it in the tank) and have a single driveshaft going through the tank interior to the steering unit, rather than 2. As a side effect, the M24 also had 4 gears in reverse, although official instructions were to put the transmissions in low to drive in reverse.
As a bonus compared to the M5, the M24 also had a special pedal on the left, where a clutch pedal would be, that pulled the transmission linkage to the Neutral position. It effectively disconnected the transfer unit from the engines, thus acting as a clutch for shifting the transfer unit on the go with only 1 lever, rather than shifting the transmissions in N, shifting the transfer unit, and going back to D.
The M24 had a little more design breathing room than the M5, which was very much developed on a “What can we make NOW, with a minimum of new tooling?” basis.
The ’48 tailfins are generally credited to aircraft like the P38, but they look a lot like the back end of this tank!
Hydromatics were harsh shifting into 2nd and 3rd gear in cars and I’m sure what ever mods they made for the tanks compounded that. I remember reading a story many years ago about a guy putting this setup in a car, it was fine under normal driving but if you got on it the shift was so hard it would snap an axle every time. Neighbor had a Sherman but his was Ford powered.
All I can say is that the selection of subject vehicles for Curbside Classic articles has really tanked!
My father was in the Canadian army between WW II and Korea. He was trained as a tank commander and told many stories of the various WW II surplus tanks they had to play with including some of these. I though he told me they had Cadillac V16s but maybe he meant 16 cylinders total between the two V8s. He said they put rubber tracks on the M5s so they could drive them on pavement. He claimed on pavement they would do close to 60 mph and they took great delight in sneaking up behind unsuspecting farmers and turning on the siren! I seem to recall him telling me that they also had some twin engined tanks with each engine driving one track independently and that you could steer them just using the accelerators (one for each engine) and if you put one in forward and the other in reverse you could turn them in their own length.
M3/M5 had its flaws, but were armored slightly better than early British cruiser tanks, and more reliable. There were so many built, they still outnumbered M24s by war’s end.
Its finest hour was probably the Battle of Kinmen in 1949, in which Nationalist M5s happened to be on the beaches when the Communists launched an night amphibious assault. PLA troops were slaughtered, possibly saving Taiwan.
The Australian Armoured Museum recently re-engined one of these with a crate 350, making it outrageously more powerful than the original.
I always enjoy your articals Aaron. An interesting companion to this might explore the Universal Carrier, it was prduced in the tens of thousands and used a Ford flathead V8 and 1940 Ford pickup back axle.
As much as I despise the modern use of the phrase, The United States of America was truly great in the WWII era. (In some respects, at least. Plenty of bad stuff was going on, as well.)
All manner of war materiel went from concept to mass production in weeks or months, not years. Production factories switched from producing consumer and commercial goods to producing anything and everything the military needed, with incredibly fast turnarounds. It really was an amazing time.
Excellent article Aaron, you answered some long-standing questions I had about these vehicles. It is interesting but perhaps not surprising that U.S. Army Ordnance favored air-cooled radial gasoline engines for tanks in the 1930’s. These aircraft-type engines were high-output, reliable, and air cooling proved to be an advantage in the North African campaign. One disadvantage was this type of engine gave U.S. tanks a higher profile than tanks with more conventional powerplants. However, this characteristic eventually proved to be an advantage when air cooled radial engines became in short supply for aircraft. The large engine bays of the M3/M5 and M4 Sherman tanks could accomodate many different engine configurations, which was a great advantage for production as we saw with the M5’s twin Cadillac/Hydramatic powertrain.
I was also wondering about that gas station in West Los Angeles. That place cold be its own Curbside Classic!
What I don’t understand about the US tank engine issue is, why didn’t they procure a chopped and derated Allison V1710? So far I have found no answers to that question online. After all, the Ford GAA V8 had similar origins and became the Army’s preferred engine for the Sherman.
Even though Allison was owned by G.M. by the time WWII broke out, it really wasn’t a very large company. They could just keep up with production for the aircraft that used the V1710 (P-38, P-39, P-40, P-63, and the odd Mustang) but beyond that Allison would have struggled. There was a project to power a B-17 derivitive (XB-38) with turbocharged V-1710’s but Allison’s production constraints was one reason the project didn’t progress beyond the prototype stage. Kind of a shame, the XB-38 was a beautiful aircraft that performed significantly better than a B-17.
The Ford liquid-cooled aircraft V-12 project didn’t progress as there wasn’t much need for it beside the Allison V-1710 and the Rolls-Royce Merlin which was also produced by Packard. Ford had done considerable work on the engine and had the production capacity to manufacture it, so it was pressed into service quite successfully as a V-8 tank engine.
Was there anything done to synchronize the shifts of the two Hydramatics? I guess it didn’t really matter much if there was a slight lack thereof.
Not per se, I don’t think, but the throttles of both engines operated together (the relays from the accelerator pedal opened them both at once from the same horizontal shaft), and because the two prop shafts were both connected to the same transfer case, the governor speeds probably didn’t differ much at all. So, I think the main variation in the shift points would just be the tolerances of the different shift valve springs and how well the bands were adjusted. It was a bit of a kludge, and I don’t suppose it did the transmissions’ notorious jerkiness any favors, but it seems to have worked out well enough.
Gasoline powered tactical vehicles like the M5 are highly explosive. A single round penetrating a fuel tank can be enough to set one off. Diesel power is much preferred from the standpoint of crew survivability. German WWII tanks were also gasoline powered so just as dangerous in theory. However they generally had better armor. Credit the Russians with getting WWII tanks right. Their T-34 was diesel powered giving crews a better survival odds. They did somewhat fritter that advantage away by carrying extra fuel in unarmored external tanks. Crew procedure was to jettison the external tanks if combat was immanent.
I never really appreciated what a difference fuel made for survivability until the 1st Gulf war. Many support units being activated had older generation gas powered M880 series (Dodge Powerwagon) trucks with the gas 318s. Before deployment, the Army made extensive efforts to see all these units upgraded to the M1008 series (Chevy K250) trucks with a GM diesel.
A lot of units initially questioned why they were suddenly given vehicles different from what their motor pool personnel had been trained on. Seeing the survivability simulations pretty much stopped all further questions.
True, and ironically the U.S. Army didn’t take many of the twin Detroit Diesel powered M4A2 Shermans in WWII due to concerns about fuel logistics. The diesel M4’s went to the Marine Corps and Lend-Lease.
This was also the thing that made submarines practical by WWI – some early subs used gasoline engines when not on battery, which was just a disaster waiting to happen. Diesel power made the concept work. It is kind of amazing that it took so long for diesel to catch on in other military applications.
Pretty neat and love all the details you provided .
Back in the 1960’s pretty much every Military Surplus store had lots of the periscopes missing here .
BIG suckers, heavy too, $5 would get you one new in the box, what the heck anyone was supposed to -do- with it is anyone’s guess .
A few years back there was one of these for sale in the midwest and under $10K, it ran and drove but those flathead Caddy V-ates smoked blue like mad .
-Nate
I have known for a long time that Cadillac V8s and Hydra Matic powered some tanks, but never knew any of the details, so this was quite interesting.
The part I always found the most amazing was how quickly the Hydra Matic went from introduction in passenger cars to the military tanks. I guess that tells us both how important ready-made components were for tank development and also how good GM’s engineering infrastructure was in those days.
I believe all Cadillac tanks were built at a large factory near the Cleveland, Ohio airport. This facility still exists and has been used as an exhibition hall known as the IX Center for many years. It was hastily built early in the WWII years. It continued to be operated by the Cadillac division of GM throughout the war and on into the early 1970s. Many generations of military tanks were built there and were used in WWII, Korea, and Vietnam. As the Vietnam war was winding down this factory was closed and the machinery and other infrastructure was sold off. My hoarder father bought much of the electrical distribution equipment.