TECHNICAL INFORMATION REPORT 3-1-2H1

OFFICE, CHIEF OF ORDNANCE
(11) April 1956

DEVELOPMENT
OF
90-MM GUN TANK, T49


90-MM GUN TANK, T49

A recurring problem of tank design is the increasing of firepower, armor protection, and mobility without a comparable increase in weight and size. During the last decade, as the potentialities of steel armor have come closer and closer to realization and metallurgy has so far been unable to provide a satisfactory substitute for steel as the basic armor material, this problem has become increasingly difficult to solve. The development of the T49 90 mm gun tank, which combines the armament of a medium gun tank with the armor protection and mobility of a light gun tank, represents one attack upon it at the medium gun tank level.

Studies conducted for several years before mid-1951 indicated the possibility of mounting a 90-mm tank gun in a 76-mm gun tank if the gun selected were a low-pressure weapon designed for firing fin-stabilized HEAT rounds; adoption of a low-pressure gun would make possible the saving of weight needed to offset the results of increasing the weapon's caliber by 14 mm. As a result, development of a smoothbore gun of this type, designated the T132 90-mm gun, was put under way, with the requirement that its tube be quickly replaceable in the field. At first it was believed that the T132 gun could be mounted in a T41E1 tank without making major changes in the vehicle or increasing its over-all weight. However, it soon was found that both a new gun mount and a new turret were desirable, and the problem then became one of designing these so that they would not increase vehicle weight. During 1950 and early 1951 work was concentrated on the development of a mount and turret which would meet all the conditions set.

In June 1951 the different phases of the work were brought together under a project for development of the T49 90-mm gun tank. The objective of this project was a lightly-armored high-speed tank of the light gun class but with the firepower of a medium gun tank, to be used principally for antitank missions.

In compliance with the quick-removal-of-tube requirement, the T132 smoothbore gun had been designed so that its tube could quickly be changed in the field. The gun was originally to be installed in the T138E1 combination gun mount of the T41E1 76-mm gun tank; however, because the T138E1 mount had been designed for a gun with a nonremovable tube and could not satisfactorily be adapted to the T132 weapon, a new combination gun mount was designed. This was the T145 mount with T87 recoil mechanism. Development of the T145 mount, in its turn, compelled altering of the T132 gun's contour so that it would fit the T145, rather than the T138E1.

The next major change in design was necessitated by the results of tests of the ammunition developed for use in the T132 gun, which tests had revealed the improbability of the gun-ammunition combination attaining the ballistic results desired. Accordingly, the design of the T132 gun was modified to call for very shallow rifling of the tube and a slight increase in chamber pressure; the revised design, designated T132E1, was nevertheless that of a low-pressure gun to fire fin-stabilized HEAT projectiles. Since this change in plans, the development of the gun has proceeded from the T132E1 to the T132E3 model. The T132E2 differs from the T132E1 only in certain modifications of the chamber, which has been further modified in the T132E3. All models from T132E1 through T132E3 have light rifling of one twist in twenty-five calibers. Each is a thin-walled gun for firing 16-pound fin-stabilized HEAT projectiles at a muzzle velocity of approximately 2,800 fps. From these models, the T132E3 has been selected as the main armament of the T49 tank.

No new HEAT ammunition is being developed for use in the T132E3 gun, which will fire the T108E40 90-mm HEAT shell. The original requirement that the T49's gun should fire only HEAT rounds has been modified, and the following rounds now under development are now specified for use in the T132E3:

90-mm HEP shell, T142E8
90-mm HE shell, T91
90-mm WP smoke shell, T92

As developed to date, the T49 90-mm gun tank is a lightly-armored full-track-laying vehicle of 25.5 ton combat weight; it is 27x(*) inches long, 124 inches wide, and 108 inches high.

[* - Last digit is illegible on binary copy. It may be 273 or 275.]

Except for turret and main armament and very minor differences in hull, the T49 tank is identical with the M41 and M41A1 76-mm gun tanks. The turret developed for the T49 is made up of arc-welded castings and plate, and is rotatable through 360° on a ball-bearing ring. An amplidyne system controls the electric motors used to traverse it; this represents a recent development, intended to replace the commonly-employed constant-pressure hydraulic traversing system. Protected by armor varying in thickness from 0.5 to 1.25 inches and mounted at obliquities ranging from 0° to 72°, the turret has space for the 90-mm tank gun, a T41E3 range finder, and a caliber ,50 machine gun on the T145 combination gun mount. The weight of the 90-mm gun is counterbalanced by radio equipment, ventilator blower, and other equipment located or stowed in the turret's rear. A pintle mount for an M2 HB machine gun is located on the turret's top.

The fire control equipment for the T49 tank includes a T41E3 range finder, a T23E2 ballistic drive, an M31 azimuth indicator, commander's, gunner's, loader's, and driver's periscopes, and other instruments needed to make fire as accurate as possible.

The manufacture of two pilot models of the T49 tank was initiated in the spring of 1952. They are now being subjected to engineering tests, which are scheduled for completion in the near future. However, in the summer of 1953 Army Field Forces indicated that they were no longer interested in this tank, their reason being that the low-pressure guns developed for its main armament could not guarantee an 88% probability of first-round hit. Because of this withdrawal of user interest, it is possible that work on the T49 will not be continued beyond engineering testing and that the tank itself will not be put into production.

TENTATIVE PRINCIPAL CHARACTERISTICS

90-mm Tank Gun, T132E3

Caliber

90 mm

Length, over-all

192.26 in

Length of bore

50 cal

Travel of projectile in bore

152.65 in

Rifling


      Length

152.775 in

      Number of grooves

32

      Twist, uniform right-hand, one turn in

25 cal

Weight of tube

970 lb

Weight of breech mechanism

390 lb

Weight of complete gun

1,440 lb

Chamber capacity-

267 cu in

Density of loading

0.57

Rated maximum chamber pressure

30,000 psi

Breechblock, type

vertical sliding

Breech mechanism

semiautomatic

Firing mechanism

percussion-inertia

Ammunition, type

fixed

Muzzle velocity

2,800 fps

Maximum effective range

2,000 yd

Perforation of homogeneous armor


      HEAT shell

12 in

Rate of fire

8 rd/min

Combination Gun Mount, T145

Weight

no information

Recoil mechanism, type

concentric hydrospring

Number of recoil cylinders

1

Recoil length


      Normal

no information

      Maximum

no information

Equilibrator, type

no information

Elevating mechanism, type

electrical and manual

      Maximum elevation

20°

      Maximum depression

-10°

Traversing mechanism, type

electrical and manual

      Maximum traverse, right or left

360°

Fire Control Equipment

Quadrant, gunner's

M1

Periscope

M13

Setter, fuze

M14 or M27

Periscopes (4)

M17

Lights, instrument (3)

M36

Drive, ballistic

T23E2

Indicator, azimuth

M31

Periscopes (2)

M20A2

Finder, range

T41E3

Mount, periscope

M93

Mount, periscope

M94

Sight, bore


Ammunition Stowage

90-mm rounds

44

90-mm Gun Tank, T49

Length


      With gun forward

no information

      With gun to rear

no information

Width

124 in

Height

108.375 in

Weight, over-all

51,232 lb

Ground clearance

17 in

Tread, from center to center of tracks

102.5 in

Length of ground contact

127 in

Ground pressure

9.6 psi

Suspension, type

torsion bar

      Wheels

no information

      Tires

no information

Tracks


      Type

steel and rubber

      Width

21 in

      Number of shoes (both tracks)

150

Armor


      Hull


            Type

cast homogeneous

            Front


                  Upper

1 in @ 60°

                  Lower

1.25 in @ 45°

            Side


                  Upper

1 to 0.75 in @ 0°

                  Lower

1 to 0.5 in @ 45° to 60°

            Rear

0.75 in @ 45°

            Top

0.5 to 0.75 in

            Floor

1.25 in (front), 0.375 in (rear)

      Turret


            Type

welded homogeneous

            Front

1 in @ 72°

            Side

1 in @ 30° to 9°

            Rear

1 in @ 0°

            Roof

0.5 in

      Gun shield

1.25 to 1 in

Armament


      Main

90-mm tank gun, T132E3

      Secondary


            Coaxial

cal .50 MG, M2 HB

            On turret

cal .50 MG, M2 HB

Communications


      Radios

as selected by Signal Corps

      Interphones

4

Engine


      Type

air-cooled gasoline

      Make and model

Continental AOS-895-3

      Cylinders


            Number

6

            Bore

5.75 in

            Piston stroke

5.75 in

            Piston displacement

895.9 cu in

            Arrangement

horizontal-opposed

      Drive from crankshaft

direct

      Induction system

supercharged

      Ignition timing

automatic advance set 10° BTC

      Horsepower


            Gross

500 @ 2,800 rpm

            Net

440 @ 2,800 rpm

      Torque


            Gross

975 ft/lb @ 2,400 rpm

            Net

900 ft/lb @ 2,100 rpm

Electrical system


      Number of batteries

4

Transmission


      Type

CD cross-drive

      Range selector control box


            Type

mechanical

            Linkage to transmission

mechanical

      Torque converter

single-stage polyphase

      Gear shift and steering mechanism


            Internal

hydraulic

            External

mechanical

Oil system


      Capacity

14 gal

      Pumps


            Type

positive displacement gear

            Number

6

            Drive

3 input, 2 output shafts

      Filter, type

air maze

Coolant

air

Fuel capacity

140 gal

Brakes


      Service brake, type

wet, friction disk

      Parking brake, type

lock on service brake

Crew

4

Performance


      Maximum speed on level

45 mph

      Maximum grade climbing ability

60%

      Maximum trench crossing ability

72 in

      Height of obstacles that can be crossed

28 in

      Fording depth

72 in w/kit, 40 in w/o kit

      Turning radius

pivot

      Cruising range

77 mi