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The Chieftain's Hatch: The Clark Hydraulic Tank

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The_Chieftain #1 Posted Oct 07 2017 - 01:31

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In September, 1950, G.L. Turner, Research Engineer of the Clark Equipment Company of Buchanan, MI, proposed in a letter to the Armored Forces liaison in Detroit a design of a new tank, they called their “Hydraulic Tank”.


“Enclosed herewith you will find a brief description of the unit as we visualized it, as well as the tentative lay-outs of the unit.


You will note that this is pictured as a one man unit, we attempted to design a two-man unit as you suggested but encountered many complications with which we were not involved when designing a one man unit. We feel that the simplicity of the driver control, steering wheel which steers through a valva and a simple accelerator would give the operator adequate time for sighting and firing.


Our conception of a 105 recoilless rifle is shown on the unit, however, it probably is not correct as far as the exact measurements of the automatic loading mechanism, etc. are concerned. Tests recently conducted verify [sic] our feeling that the hydraulic drive would be ideal as a motive power and would precisely traverse the entire unit.”



The narrative and description was more or less as follows:


Generally, it is believed that a small, flexible tank which can carry a heavy recoilless gun would be an advantageous vehicle.

                Many of this type of vehicle could be built, shipped and supplied for use at distant points and could carry much fire power in from the sea or air. This tank would onley weight 6-7000lbs and could protect itself with its fire power, speed, flexibility and the greater number which could be put into the field.

                It could be used as a fighting vehicle in motion or as a static field piece. A 105mm recoilless rifle is shown, but flame throwers, etc., could be used on alternate tanks.

                The quantity that could be put in the field plus such features as

  1. Noiseless tracks.
  2. Traversing complete unit.
  3. One or possibly two man unit.
  4. High Flotation.
  5. Easy Maintenance
  6. Poor target
  7. Low Cost
  8. Surprise element in a run, etc.
  9. Ease of concealment.
  10. Ambush vehicles.
  11. Ideal for defilate firing.
  12. Ease of recovering from battle field.
  13. Unit replacement.

                 The above points have been considered and it is felt that such a unit would be of merit.

                Many of these thoughts are not new; however, the drive makes possible this grouping of characteristics.

                Doubtlessly the Field Forces could add much to the track, suspension, weapon, tactical use etc. Perhaps a combination of thoughts could result in a very successful tank.


                Tracks and Suspension.

                The proposed tracks are one piece rubber with cables molded into them. The connector on each track will be one pin locked in place. Each end of the track will have one side of a “piano hinge” which in turn is connected to the cables and molded into the rubber.

                A raised rib in the center of the track will fit into a groove in the driver, front idler, and the boggies [sic]. The boggies [again, sic], driver and idler will be the full width of the tracks (11”;). If a track were lost, the width and diameter of the driver, idler and boggies [sigh] would support the unit under some conditions.

                The drivers will be fixed to the hull, no spring suspension. The front idlers will be sprung suspended with the track take-up spring on the suspended arms. Should the fixed drivers be considered likely to give too rough a ride, rubber could be interposed between the driver hubs and the show, upon which the track might ride.

                The track contact area will be approximately 12sq ft. This high floatation is used to reduce the power required to pivot the tank by reversing a track. A practically noiseless drive should result.

                No drive sprocket will be used. The wrap of the track around the driver should be sufficient.



                The drawings show a 105mm recoilless gun mounted on the tank as the major weapon and a .30 cal. machine gun or an anti-personal [sic, yet again] weapon.

                The 105mm gun is so mounted on a hydraulic ram that it can be raised and lowered by a hand displacement cylinder connected to the ram. When the gun is in the traveling position, it is aligned with the vehicle so that the direction of travel is in the direction of firing. A link connected to the magazine would adjust the elevation when the ram is raised or lowered. When the link is released, the gun can be raised on the ram high enough to give 360° rotation by using the traversing mechanism and a separate elevation mechanism.

                 The reason for fixing the gun in the traveling position is that the complete tank can be accurately traversed similarly to a turret. This will be covered under drive.

                 Angles of elevation should be approximately 25° down and 45° raised.

                 The automatic loading device is shown and an armored outside magazine contains approximately 20 rounds of 105mm.

                 Sights would be in line with the driver’s normal line of vision. The free hand of the driver adjusts the elevation.

                 The .30 cal. machine gun would be belt-fed from a box. The driver will be able to fire the machine gun through a 180° traverse from driving position. Reload will be possible from the drivers seat.



                 The hull will be approximately 9 ½ feet long, 6 ½ feet wide, and 5 feet high.

                 The armor plate will be ¾ inch on the side and front, ½ inch on the fenders, 1  ½ inch under the driver, and 1 inch over the driver. The main plate will be located to protect the driver rather than the vehicle. Side hits in most cases have to penetrate both the ¾ inch and ½ inch plate.

                 The escape hatch would be spring loaded so when tripped, would give driver immediate exit. The Engine compartment would be easily opened and make the engine easily accessible for repair.

                 Adequate vision would be given the operator.

                The armor is for anti-personal [Sic. Well, he’s an engineer, not an English teacher] protection basically.



                 The weight of the tank is estimated at approximately 6,000lbs, therefore approximately 60hp will be required to drive the vehicle. An air-cooled engine is proposed. The engine in turn will drive a vane type variable displacement hydraulic pump which will drive through valving two vane type hydraulic motors. One motor will drive each track through a gear reduction into the driver. The pump will deliver a maximum volume of 80GPM. The variable pump will automatically reduce this volume and give a torque multiplication of 3 to 1 at a dead head pressure of 2,000psi. This type of drive is being used on one of our vehicles which will be in production in December this year.

                No intercooler other than a 25 gallon oil sump is required.

                 A dividing valve will regulate the relative flow between each drive motor controlling the steering and also give a forward direction to one track and a rearward direction to the other, thus traversing the vehicle.



 Here’s what it looked like. Something to inspire fear into the hearts of the enemy, no doubt.


Detroit Arsenal then forwarded on the recommendation to the chiefs of Armor and Infantry boards. At the time there was a proposed requirement for an “Infantry Fighter”, which, from inference, appears to be an early concept of Infantry Fighting Vehicle. The file contains only the response from Fort Knox, as below:


It is believed that there is no tactical requirement for a vehicle with the outlined characteristics as a replacement for existing tanks in any armored units.

 There is nothing presented in the concept of this vehicles which alters the position of The Armored School with reference to the Infantry Fighter as expressed [earlier]

1) The concept of armored warfare, as generally accepted throughout the world, envisages an arm of mobility, armor-protected firepower and shock action which is to be used in mass. While the midget hydraulic tank may exceed the mobility of the conventional tank, it is definitely lacking in armor protection for its firepower, and its shock action appears to be completely lacking. The effect of massed armor is psychological, as well as physical, and the psychological effect of this midget tank on the enemy appears to be negligible. Further, the low velocity weapon of this vehicle cannot compare with the accuracy and one-shot killing probability of the high velocity gun of the tank.

2) Since the main armament is fixed in a traveling position and the driver has restricted vision, the field of observation and fire of the vehicle is dangerously limited. In addition, if it is a one-man unit, the driver is of necessity pre-occupied with driving the vehicle and cannot seek out the enemy either visually or with reconnaissance by fire. As compared to the conventional tank, the limit of visibility from a height of less than five feet is greatly reduced. This is vitally important in engaging surprise targets which may appear on the battlefield.

3) As an offensive weapon, employed in reinforced units, this tank does not meet the accepted standards of seeking the enemy to destroy him. It appears that this vehicle is conceived on the idea that the position of the enemy tank is known.

4) It is impractical for one, or even two, men to be charged with the responsibility for first echelon maintenance of such a vehicle to include its power plant, weapons and communications.

5) Psychologically, it is a known fact that a single individual is not nearly as courageous as a team of two or more soldiers.

This vehicle may have possibilities as the replacement or supplement for the present, man-carried, close support infantry weapons such as the recoilless rifles.


Thus ended the proposal by Clark. They did actually end up with the occasional government contract, the M9 Armored Combat Earthmover, for example, was one of their products, so I guess they did return to reality in their area of competence.


Pretty much patently the idea was complete foolishness, though credit to them for thinking outside the box. The idea of aiming the gun by movement of the entire vehicle (although optional, by the description) certainly has S-tank shades, but even at that, the idea was implemented in the Char B1, so it's not entirely novel or futuristic.

The 105mm is not a typographical error. The 106mm recoilless rifle is in fact a 105mm, they just changed the name to avoid confusion with the standard 105mm rifles which were being played around with at the time.

Ravger87 #2 Posted Oct 07 2017 - 18:24


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From the initial description I was expecting something along the lines of a one man S-tank, this armed Mini Cooper picture was a surprise.  I have to say though, it does look like something you would imagen originating in the 50s.  It wouldn't look that out of place on the cover of a 50s era sci-fi paperback, movie poster, or comic book.

Buttknuckle #3 Posted Oct 07 2017 - 21:04


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I suspect the designers imagined something like fighter planes for the ground, and envisioned squadrons of these things swarming around causing havoc.

Vexant #4 Posted Oct 07 2017 - 22:27


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On a less-than-serious note, it's kinda cute.  I could see tankers driving them in from suburbia to their state-side assignments.


VooDooKobra #5 Posted Oct 07 2017 - 22:33


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looks like a cooper mini with a gun strapped to the top.  where is mr bean when you need him?

Hephaestus76 #6 Posted Oct 07 2017 - 23:06


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Well,this is an interesting concept. Not sure it would have worked but.... 

What I do find interesting is the M9 A.C.E. was designed by them and they did use hydraulics to steer that when it is in earth moving mode. There is a bow tie style steering control for road mode and 4 levers that control the bucket, blade and the front of the vehicle ( think low rider style). The levers worked the front of the machine independently up or down per side so you could level out the main battle tank firing position being dug. Only protection you had was a smoke screen, the mold board on the front and whatever weapon you carried at the time. We had to qualify using the M-16, 9 mm, and a 45 mm grease gun. 

MickTheGti #7 Posted Oct 07 2017 - 23:27


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I could have sure used this once in a while on 101 in Silicon Valley.  Very nice to have so much 105 lying around the Bay Area 

RLBell #8 Posted Oct 08 2017 - 01:50

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This machine evokes enough of the M50 Ontos that Clark may have been ahead of its time and thinking too small.

yuyin2014 #9 Posted Oct 08 2017 - 02:48


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No cacho nada aquí papuuuu

NK_33 #10 Posted Oct 08 2017 - 15:41


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So, when is it getting released as a premium, and what tier will it be?  ;)  I know no RRs in WoT.


I can imagine this would be a maintenance problem with either a unified hydraulic system with check valves all around to prevent a hit in one component from 'bleeding out' the entire reservoir.  Talk about overloading one person: gunner, driver, loader, radio operator and commander.

Boomslanger #11 Posted Oct 08 2017 - 16:19


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View PostButtknuckle, on Oct 07 2017 - 12:04, said:

I suspect the designers imagined something like fighter planes for the ground, and envisioned squadrons of these things swarming around causing havoc.


Frankly, although you cannot take the fight to the vertical plane, a lot of tank skirmishes that end up in melees do have the properties of a dogfight  I think if those harmless-looking tiny tanks were introduced in our game (a lot of silly theoretical tanks do exist in WoT especially in the low tiers. What is one more? a quick turning tank with a big [edited]gun that looks funny till it out turns your tank and comes around dodging shells and gets at you firing a 105mm HEAT shell to make you laugh? I'd be one of the first to buy the damn thing!! :)   I give below The salient points of "dicta boelcke" taught to every fighter combat pilot in elementary school. Of course, it has a lot of Ariel References The use of your imagination to apply it on the ground with combating tanks is requested :) Actually the more I read it (Dicta Boelcke) the more I see how cool it is to apply the rules while playing! these rules have helped me quite frequently especially rules 1.1 to 1.3 and I die too frequently and early in a game making me a very mediocre player indeed probably because I do not follow rule no 1.4 " When attacking make sure you know and remember your line of retreat and disengagement'. I have cut and pasted the rules from wickipedia.org the way it reads in my textbook is very different. Do tell me what you think about the applicability of the rules... In rule 1.1 I interpret 'the sun behind you" as equivalent to using the slope of the terrain or other terrain features. Also, we fly various attacking or defending formations and one of the most popular one these days is called "the solitary pair' where two aircrafts fly one behind another. one a little to the left or right of the other and separated by a distance of usually one and a half times the turning radius of the first aircraft in dissimilar aircraft type. The reason is that aircraft in the front can turn into any aircraft that may threaten the aircraft at the rear. The tactical advantage of two tanks moving to attack in this fashion is obvious...



Edited by Boomslanger, Oct 08 2017 - 16:43.

Master_Beater #12 Posted Oct 08 2017 - 19:57

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What tier will this new premium tank be? Tier 8 with a 105 canon?

Destroyer_Monssen #13 Posted Oct 09 2017 - 17:00


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View PostRLBell, on Oct 07 2017 - 18:50, said:

This machine evokes enough of the M50 Ontos that Clark may have been ahead of its time and thinking too small.


I am reminded more of the German Weisel but agree that Clark may have been a visionary.

Nihtwaco #14 Posted Oct 11 2017 - 03:42

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At the time we did have a 105mm RR M27.


https://www.globalsecurity.org/military/systems/ground/m27rclr.htm  Projectiles had a long tail boom much like a RPG 7 Projectile. The Follow on BAT program developed the M40 RR which had much in common on the projectile side with the then new 105mm M67 version of the L7 to avoid confusion in the supply chain the M40 was designated as a 106mm.

armando30 #15 Posted Dec 28 2017 - 21:58


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I do not know if what I am about to ask was already talked about in this section of the forum, to which I am new at following, but this tidbits about "funny" ideas are interesting however I would like to ask if you do plan to ever talk about in detail in the many plans, by the americans, to have nuclear-powered tanks and even cases of entire nuclear-powered armoured convoys, if this has already been talked about I should apologize and search better for it


The_Chieftain #16 Posted Dec 29 2017 - 00:06

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It has not really been discussed, but pretty much most of the information I know of is in Hunnicutt. Firepower, as I recall.  It that there is much info.

KanataKonoe #17 Posted Dec 29 2017 - 20:59


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That picture looks like a С3Д with a 105mm gun strapped to the top. And made with tracks instead of tires.

WalkerSteele #18 Posted Jan 02 2018 - 18:07


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Sounds like a "skid-steer" with a large gun; the track and suspension appear to be the same, that part at least is a good idea


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