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.
1. Chamberlain, P. and Ellis, C. “British and American Tanks of
World War II”. Arco
2. Crison, F.W. “U.S. Military Tracked Vehicles”. Motorbooks International,
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
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
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
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