ARTICLES

ARTICLE 1       AMERICA’S SUPER HEAVY TANK

As World War II was drawing to a close, all the major powers were developing monstrous super tanks of 100 tons or more in weight. The Germans had several prototypes of the Super Heavy Tank, The “Maus” (Porsche 205), weighing in at 188 tons and the Henschel E-100 at 140 tons. The British were developing the Model A39 “Tortoise”, and the Americans had their own version of the Super Tank designed to break through the Siegfried Line Defenses expected to be encountered in Germany. The proposal called for mounting a new HV 105mm T5E1/67 gun in a tank with 8" frontal armor. This gun could effectively penetrate concrete fortifications.

Work began on this Super Heavy Tank, designated as the T28, in the spring of 1945 at the Pacific Car and Foundry Co. Initial plans called for 5 prototype vehicles with an eventual total of 25 to be built. However, the war drew to a close and only 2 were ordered. These prototypes were evaluated at both the Aberdeen Proving Grounds and the Fort Knox facilities.

This tank was very heavily armored, with 12” on the front of the hull, 5-1/4” on the lower front hull and 2-1/2” on the sides. The 1 ft of frontal armor could provide protection against the famous German 88mm gun at a range of 1100 yds. The hull was cast steel and extended 2/3 of the  length of the track assembly set to the rear. The suspension system and lower hull were covered with heavy skirts 4" thick. A turtle shaped superstructure had a cupola for the commander and a ring mounted caliber .50 AA machine gun. The tank had a rather low silhouette. The overall height was only 9" 51/2"  at the top of the hatches. 

This tank did not have the normal turret. Instead, a new 105mm (T5E1) gun was set into a ball shaped  111/2"thick mantle. This gun could achieve muzzle velocities up to 3,700 ft/sec., firing high velocity armor piercing rounds. It was a formidable weapon. The traverse was limited to 10 right and 11 left. Elevation was from -5 to +19.5 . When traveling, the gun was locked at the maximum elevation. Without a turret,  this   vehicle more closely resembled a Self- Propelled Gun and thus was redesignated as the T95 Gun Motor Carriage in 1945. Later, in June of 1946, the vehicle  was redesignated as Super Heavy Tank T-28.  The only secondary armament  carried was a caliber .50 machine gun mounted above the commander’s hatch. The tank was operated by a crew of 4.

This vehicle was the largest AFV of American design in WWII. It was almost 15’ wide, 36’ long and weighed 190,000 lb. (95 tons). Because of its huge size and weight, it was equipped with 4 sets of tracks, two on each side of 19-1/2” width each. This most unusual arrangement was needed to lower the ground pressure to 11.7 lbs./sq.in. Each track assembly was made up of two complete horizontal volute suspension systems (HVSS). In order to reduce width and weight, the outermost tracks could be removed when the tank was being transported. To assist in this Herculean task, the tank carried two hydraulically assisted winchs mounted at the rear of the tank. Each track assembly weighed almost 25 tons, and two could be linked together side by side to form a unit which could be towed behind a prime mover or the tank itself!  It took a crew almost 3hrs. to make this change. The running gear included a total of 64 20-1/2” wheels with rubber backed steel tracks 19-1/2” wide and rear drive with support rollers and front idler.

This monster was powered by an anemic single Ford GAF V-8 gasoline engine developing only 410 hp @ 2600 rpm. The power to weight ratio was only 5.37 hp/ton. The power train consisted of a Torquematic transmission with 3 speeds forward and 1 reverse. Brakes were an external contracting type. Steering was by controlled differential. With this power train,  the tank was badly underpowered and could manage speed maximum speed of  only 8 mph. Four fuel tanks held 400 gallons of gasoline, allowing a range of 100 miles. The vision and sighting equipment consisted of two periscopes type M6, one type M10E3 periscope and 1 3X telescope M8A1 type T.

There was no stabilization of the main gun. A total of 62 rounds of 105mm ammunition was carried. Manual loading was required resulting in a rate of fire of only 4 rounds per minute.

With its enormous mass, mobility was limited. Performance included: maximum grade 60 % , maximum vertical wall 24” and maximum fording depth 47”.

Two vehicles underwent intensive evaluation trials until 1947 by which time the superior heavy tanks, T29 and T32, were available.  The T-29 mounted the same gun in a conventional rotating turret. The program was terminated in October of that year. At that time, this tank with its 105mm gun was the only Western tank capable of opposing the Soviet JS-3. Consideration was given to producing this  tank for the contemplated invasion of Japan.

What became of these behemoths? It was reported that one tank burned up during trials, and the other was broken up for scrap during the Korean War. Yet, in 1974, a T28 was found sitting on a range at Fort Belvoir, Virginia. It is still a mystery as to where this tank spent the years 1947 to 1974. The tank was dismantled and shipped to the General Patton Museum at Fort Knox, Kentucky, where it is on prominent display.

Note: The author wishes to thank Mr. David Haugh for his generosity in providing a list of key references for this article.

References:

1. Chamberlain, P. and Ellis, C. “British and American Tanks of World         War II”. Arco Publishing, 1969.
2. Crison, F.W. “U.S. Military Tracked Vehicles”. Motorbooks International, 1992.
3. Characteristics Sheet. Detroit Arsenal R&D Division. November, 1948.
4. Publication A 35309 A, 105mm GMC T95. Aberdeen Proving Ground. April, 1946.
5. Hunnicutt, R.P. "Firepower: A History of the American Heavy Tank"
 Presidio Press 1988.

Thomas M. Tencza
May 15, 2000

Article 2:                                        MBT70
                        Dismal Failure or Technological Marvel?

In 1963 West Germany and the U.S.A. entered into a joint development agreement to build the "Tank of the Century" . It was to include all the available state-of-the-art technologies to allow it to serve to the end of the century. It was designated as the MBT70 by the U.S. and MBT/Kpz-70 by the West Germans. From the onset, there were significant disagreements as each side endeavored to protect its own defense industries by getting as large a piece of the pie as possible. Disagreement arose over such simple matters as the type of technical drawings and whether metric or SAE treads be used on fasteners in the tank. A compromise allowed the U.S. to use SAE while the Germans stayed with metric, requiring two different sets of tools for maintenance. By 1970 the partnership broke up after completion of a few pilot models. By that time costs had skyrocketed and the U.S. Congress cut off additional funds.

Both US. and German versions were produced which differed significantly. The engine in the U.S. version used the Continental AVCR air-cooled 120° V-12 variable compression diesel developing 1470 hp designed to operate on multi-fuels. The German version used the 12 cyl. MTU MB873 Ka water-cooled multi-fuel engine developing 1500 hp, which together with its drive train could be replaced in 15 minutes. Both engines complied with NATO's policy of being multi-fueled to reduce logistical problems in time of war. There were significant differences in the main armament as well. The U.S. version was  equipped with a troublesome 152mm gun/missile launcher system which fired the 152mm M409 round with a HEAT anti-tank warheads. Even this round was unique in that it used a combustible cartridge case. This launcher could also fire a missile which when launched fired off its rocket motor to reach speeds in excess of 2600 mph . It  had an effective range of 5700 yds. It was guided by an IR beam controlled by the gunner. Development of this Shillelagh missile system was plagued with problems in both the  M551 Sheridan and the M6OA2.

The Germans were skeptical of this system and designed a second turret equipped with the Rheinmetall 120mm gun. The MBT design included an autoloader in both versions in order to reduce crew size to 3 and reduce the height of the hull . All 3 crew members were situated in the turret with the driver in his own independent counter-rotating cupola which was designed to face forward regardless of the position of the turret. This proved to be a major problem as drivers complained of disorientation and motion sickness. One advantage of the location was that it was close to the center-of-gravity, giving the MBT70  a superior ride performance by reducing the vertical pitch input to the driver. This reduced pitch input to the driver allowed him to drive at higher speeds before the dynamic ride level he experienced exceeded the US Army's limit of 6 watts of average absorbed power in the vertical direction. This permitted cross country speeds much better than the M60A2 in tests carried out at the APG facility. 

In 1969, tests of the MBT70 vs. the M60A1E2 (M60A2) were conducted  at APG.  Both tanks were equipped with a 155mm gun/launcher.  The  longer barrel of the MBT70 allowed it to fire hypervelocity KE ammo. In bridging tests, vertical obstacle tests, the MBT70 was clearly  superior.  It was 3 times faster on the 60% grade and in the acceleration it reached 30 mph in 18 sec. vs. 43 sec. for the M60A2.  Cross- country tests in various terrains showed the MBT70 to be clearly superior.  In simulated combat exposure tests, the MBT70 had 1/3 less exposure time than the M60A2 and was 30% faster on a 6-mile course. The study concluded that the MBT70 was superior in every aspect tested.  Its higher hp gave better speed and acceleration and its variable hydropneumatic suspension enabled it to take advantage of its powerful engine for greater speeds over rough terrain and yet crouch lower than the M60A2 in a defilade position to reduce target area.  The engine and suspension appeared to be the decisive factors in the unusual record-setting performance of the MBT70 during these comparisons.   

This tank was and still is very impressive. It is 29' 8" long with gun forward and only 7' 5" at normal operating height and 11' 15" wide. The thick gun mantlet and huge sloping turret are very impressive. The turret was equipped with a pop-up gun mount carrying a remote controlled 20mm cannon. Eight single-barreled smoke grenade launchers were mounted on each side of the turret.

Another innovation on this tank was the complex variable height, Teledyne Continental Model 2812 dual piston hydro pneumatic suspension system , which enabled the tank to drop its overall height to reduce its silhouette in a static firing position. It could drop  to a clearance of only 4.5 inches and then to rise for cross country mobility with a maximum clearance of 28 inches. This was an engineering and mechanic's nightmare with leaks and problems. The controls permitted an adjustment of front/rear, left/right or any combination thereof. 

The turret was fully stabilized; the tank was equipped with a laser range finder, a ballistic computer, environmental control / life support system, night sights, spaced armor and advanced power train. The quality control assurance and reliability were set at a standard never before realized.

The MBT70 embodied such excellent safety features as spaced armor to defeat incoming rounds, with bulkheads, fireproof doors and blow-out type sections in the ammunition storage area to minimize crew injury when a hit was received. Self-sealing fuel tanks were also included. The MBT70 could travel 400 miles on 400 gallons of fuel, ford an 8-foot deep stream and climb a 70% grade or cross a 9-foot trench. The combat weight was 105,273 Ibs. or 52.6 tons.

The first prototypes were presented simultaneously in both Germany and the U.S.A. in July 1967. Technical problems abounded and delays and costs skyrocketed. At that time the cost of a single MBT70 was estimated at U.S. $1 million, whereas an M60A2 cost about $220,000. Congress grew increasingly restive after spending more than $400 million in R&D and in 1969 denied any further funds. The Army made a valiant attempt to salvage the program with the XM803 less expensive version incorporating many of the desirable features of the MBT70. Six were to be built. Instead, an MBT70 was converted to XM803 specifications and this prototype still exists at Fort Knox, Kentucky.

When the joint project disintegrated, both countries began to work on austerity versions of the Main Battle Tank to utilize some of the advanced technology developed. The American prototype was designated initially as the XM815 but later designated as the XM1 which eventually became the M1 Abrams.

The Germans developed the Leopard 2(AV) which was sent to Aberdeen where it was evaluated versus the XMl prototypes. In January 1977, the U.S. formally announced it had selected the XMl over the German Leopard 2 prototype, not an unexpected decision. 

Was the MBT70 born premature? The technology employed was new and experimental with major design flaws and overruns. The problems encountered incorporating so many new systems widened the gap between the partners. Joint ventures always result in differences between the partners and this one was no different. Some differences were minor, but others were major such as the American insistence on using the ill-fated Shillelagh system while the Germans wanted the flexibility of a projectile firing cannon. Interestingly, the Rheinmetall 120mm cannon was later adopted for the Abrams M1A1 tank. This program showed what a modern tank would cost. The XM1 program that followed cost more than the projected costs of the MBT70, even without all the high tech features. 

The MBT70 on this web site and the specimen exhibited at Aberdeen are still very popular with visitors.

Thomas M. Tencza
June, 2001

References:
1. "Tanks of the World", David Miller, MBI Publishing, 2000.
2. "U.S. Military Tracked Vehicles", Fred W. Crismon, MBI Pub., 1992.
3. "Museum Ordnance" magazine, January 1992.
4. Personal Communication , R. Criswell, 2001.
5. "MBT70 & M60A1E2 Interim Field Comparison", Vintage Video, 
    VHS-141.