TECHNICAL INFORMATION REPORT 3-1-2H4

OFFICE, CHIEF OF ORDNANCE
February 1956

DEVELOPMENT
OF
90-MM GUN TANK, T69 (U).

RELATED TIR'S

5-54

TIR 3-1-2

Development of Medium Gun Tanks

4-54

TIR 3-1-2H1

90-mm Gun Tank, T49


TIR 3-1-2H3

90-mm Gun Tank, M48A2 (T48E2)


TIR 3-1-2H5

90-mm Gun Tank, T95

4-54

TIR 3-1-2J1

105-mm Gun Tanks of the T54 Series


TIR 3-1-2J2

105-mm Gun Tank, T96


90-MM GUN TANK, T69

In the restricted space of a tank turret the manual loading of heavy rounds of ammunition becomes so difficult as to nullify the advantages of the employment of a rapid-fire high-velocity gun. One of the major problems of tank design, therefore, is the provision of an automatic loading mechanism for the tank gun. The need for this was recognized as early as May 1946, when a general development project for this type of equipment was initiated. When the development of the T42 90-mm gun tank, the first really new postwar medium gun tank, was approved in May 1949, automatic loading was included as a requirement to be met if possible.

Unfortunately, the design of an automatic loading mechanism suitable for installation in a conventional tank turret could not be carried out successfully. In part, this is because of the very circumstance that makes such a mechanism most desirable, namely, the limited space available in a tank turret, but it is also because in a conventional turret the position of the gun relative to the turret is constantly changing. In any event, the T42 tank was developed without the automatic loading feature. User-tested in 1952, it was considered by AFF to have several basic deficiencies, correction of which would have necessitated a fairly complete redesign. Partly for this reason and partly because the T48 (now the M48) 90-mm gun tank had meanwhile been developed and put into production, in October 1954 the T42 tank project was terminated.

During one of the discussions of the design of the T42 tank, it had been suggested that the problem of providing automatic loading for tank guns might be solved by development of a trunnion-mounted ball-type turret that could be elevated and depressed as well as traversed. In this type of construction, now generally called an oscillating turret, the gun could be rigidly fixed in position and, because there could be no movement as between,the gun and the turret (other than that of recoil and counterrecoil), the installation of an automatic loading device is greatly simplified.

In March 1951, accordingly, Ordnance initiated a project for the development of a trunnion-mounted turret with a 90-mm gun of the T139 (now the M41) type, automatic loading equipment, and simplified fire control, the entire assembly to be suitable for mounting on the hull of a T42 tank. The new turret was to be operable both by power and manually in such a way as to give the gun unlimited traverse and any elevation between 20° and -10°. In addition to the main armament, there was to be a coaxial machine gun and another machine gun on the turret roof. In October 1952 the vehicle to be developed was designated the T69 90-mm gun tank.

Concentrated work on the T69 tank was begun in May 1951, but partly because of delays in furnishing the contractor with equipment to be provided by the Government, it proceeded slowly. Six different turret designs were evaluated by APG and AFF before one was selected for development. Even then it was necessary to study in detail the ballistic protection afforded by this design; this was done by actually casting several ballistic turrets and shipping them to APG for tests. Only after these matters had been settled was the final assembly of a pilot model begun. This model, utilizing the hull of one of the six T42 tank pilot models, was completed at the beginning of 1955, and shipped to APG for engineering tests, which began in May and are continuing.

The T69 90-mm gun tank, though mounting virtually the same armament as the recently-adopted M48A2, weighs only 76,000 pounds when combat loaded, which is 27% less than the weight of the M48A2. It is also somewhat smaller than the latter. The performance characteristics of the T69 tank have yet to be established, but it is driven by the same engine and transmission as the almost equally-heavy T42, which has approximately the same maximum speed and grade climbing ability as the standard 90-mm gun tank. Because of its smaller fuel tanks, however, the cruising range of the T42 is considerably less than that of the M48A2. One obvious disadvantage of the T69 is that it can stow only 38 rounds of 90-mm ammunition, as compared with the 64 that can be carried in the M48A2.

The T69 turret is basically a steel casting bearing on a turret ring 73 inches in diameter. The casting presents surfaces of high obliquity in order to deflect missiles and achieve a low silhouette. Mounted on trunnions, the turret is normally actuated by a hydraulically-powered traversing and elevating mechanism, but independent manual operation is available for use if the hydraulic system should fail. The turret is fitted with a platform, suspended from the turret ring, which affords storage space and contains part of the electrical and hydraulic apparatus. The top of the turret is covered by a large hinged access cover equipped with commander's and loader's escape hatches. This cover, which is raised and lowered hydraulically, not only affords quick exit in combat but also facilitates the loading of ammunition and supplies, the making of necessary repairs, and the installation of new parts; it also permits the automatic loading equipment to be installed or removed without disassembly. Seats for the commander, loader, and gunner are secured to the sides of the turret.

A T178 90-mm gun is mounted in the T69 turret in a conventional concentric recoil mechanism. It is a standard M41 tank gun with the breech modified to permit automatic loading. A caliber .30 machine gun is mounted coaxially with the 90-mm gun, and can be fired electrically by the same controls that fire the main armament. A cal iber .50 machine gun, for either ground or antiaircraft use, is emplaced in a pintle mount on the access cover; it is controlled and fired manually. Provisions are also made for carrying a submachine gun, a carbine, and a grenade launcher in the tank.

The automatic ammunition-handling equipment is rigidly installed on the longitudinal center line of the turret and consists chiefly of a magazine and a loading mechanism, permanently interlocked. The magazine holds eight rounds of ammunition in a rotating spider and is so designed that the gunner can select any one of three types of round for loading. The loading mechanism, which is hydraulically driven, brings a rammer into position, pushes a round into the gun|s chamber, and returns the rammer to the magazine before the latter is permitted to index the next round. An ejection chute is mounted above and in line with the loader, and cases are ejected through a hydraulically-operated door in the rear center of the bustle. The cyclical rate with this automatic loading equipment is 32 rounds a minute. In an emergency, the loading operations can be performed manually.

The T42 tank hull, on which the T69 oscillating turret is mounted, is constructed in two sections. The forward of these, a homogeneous armor steel casting, houses the fighting and driving compartments, while the rear section, of welded armor plate, houses the engine compartment; the two sections are joined by a vertical weld.

The T69 tank is rear-sprocket driven with ten dual road wheels suspended by individual torsion bars. The T95 tracks with which it is fitted are steel-and-rubber single-pin tracks 24 inches in width, designed to accommodate detachable rubber pads. The vehicle is powered by a 6-cylinder air-cooled gasoline engine directly connected to a cross-drive transmission. The engine, Continental Model AOS-895-3, is supercharged and develops 500 horsepower. The Model CD-500-3 cross-drive transmission is a combined hydraulic torque converter, steering, and braking unit.

The primary fire control system for the T69 tank consists of equipment at two different stations. A T46E2 range finder and a T33 range drive are located at the commander's station, and an M20 (T35) periscope, a T184E3 periscope mount, and a T32 range drive are at the gunner's station. The T46E2 range finder, which is a 10-power binocular instrument employing the stereoscopic ranging principle, is used to determine the range to the target, while the T33 range drive enables the required superelevation to be introduced into the range finder. The T32 range drive, on the other hand, provides a means for introducing superelevation into the M20 periscope, which is used for observation and, in conjunction with the T32 range drive, to lay the gun. This periscope has two built-in optical systems, one 6-power, the other unity-power. The T184E3 periscope mount holds the periscope and the range drive to the turret. Because the fire control equipment, mounted on the turret, moves with the gun tube and the turret, the linkages normally needed to transmit gun elevation to the fire control equipment are unnecessary; the gun elevation is automatically introduced when the gun is layed.

In addition to the M20 periscope, periscopes of three other types are installed in the T69 tank. Six M26 (T25) periscopes are arranged around the commander's hatch to give 360° vision. Five M27 (T36) periscopes are supplied for the driver, and one M13 periscope serves for the loader.

In order that the tank may be used for artillery support, an M13 elevation quadrant and an M31 azimuth indicator are also provided for laying the gun for indirect fire.

The engineering tests of the T69 tank are expected to be completed by April 1956.

TENTATIVE PRINCIPAL CHARACTERISTICS

90-mm Tank Gun, T178

Caliber

90 mm

Length, over-all

193.21 in

Length of bore

50 cal

Travel of projectile in bore

156.4 in

Rifling


      Length

152.77 in

      Number of grooves

32

      Twist, uniform right-hand, one turn in

25 cal

Weight of tube

1,582 lb

Weight of breech mechanism

679 lb

Weight of complete gun

2,370 lb

Chamber capacity

300 cu in

Density of loading

0.83

Rated maximum chamber pressure

47,000 psi

Breechblock

vertical sliding

Breech mechanism

semiautomatic

Firing mechanism

electric

Ammunition, type

fixed

Performance


      Muzzle velocity (AP)

3,000 fps

      Muzzle energy

1,503.6 ft/ton

      Muzzle energy/weight ratio

0.637:1

      Maximum effective range

2,000 yd

      Perforation of homogeneous armor @ 0°


            AP shot @ 1,000 yd

6.2 in

            AP shot @ 2,000 yd

5.9 in

            HEAT shell

12 in

      Spalling of homogeneous armor


            HEP shell

4 in

      Rate of fire

30 rd/min

Combination Gun Mount

Weight

no information

Recoil mechanism

concentric hydrospring

Number of recoil cylinders

1

Recoil length


      Normal

no information

      Maximum

no information

Equilibrator

no information

Elevating mechanism

hydraulic and manual

      Maximum elevation

15°

      Maximum depression

-9°

Traversing mechanism

hydraulic and manual

      Maximum traverse, right or left

360°

Fire Control Equipment

Range finder

T46E2

Range drive

T33

Periscope

M20 (T35)

Periscope mount

T184E3

Range drive

T32

Elevation quadrant

M13

Azimuth indicator

M31

Periscope

M13

Periscopes (5)

M27 (T36)

Periscopes (6)

M26 (T25)

Ammunition Stowage

90-mm rounds

38

90-mm Gun Tank, T69

Length


      w/gun forward

323.75 in

      w/gun to rear

280.375 in

Width

140.812 in

Height

112.875 in

Weight, over-all

76,000 lb (approx)

Ground clearance

17.125 in

Tread, from center to center of tracks

111 in

Length of ground contact

130 in (approx)

Ground pressure

12.2 psi

Turret

oscillating

      Diameter of ring

73 in

Suspension

torsion bar

      Wheels

26 in

      Tires

26x6

Tracks

steel and rubber, T95

      Width

24 in

      Pitch

6

      Number of shoes (both tracks)

152

Armor


      Hull

cast homogeneous

            Front


                  Upper

4 in @ 60°

                  Lower

4 to 2.5 in @ 54°

            Side


                  Upper

3 to 2.5 in @ 0°

                  Lower

1.5 in @ 0°

            Rear

1 in @ 60° and 50°

            Top

2 in

            Floor

1 to 1.5 in

      Turret

cast homogeneous

            Front

4 in @ 60°

            Side

no information

            Rear

equivalent to 5.75 in @ 40°

            Roof

no information

            Gun shield

no information

Armament


      Main

90-mm gun, T178

      Secondary


            Cal .30 MG, coaxial

M1919A4E1

            Cal .50 MG, on turret roof

M2 HB

            Cal .45 SMG

M3A1

            Cal .30 carbine

M2

            Grenade launcher

M8

Communications


      Radios

to be determined

      Interphones (4)

AN/UIC-1

Engine

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 cu in

            Arrangement

horizontal-opposed

            Compression ratio

5.5:1

      Horsepower


            Gross

500 @ 2,800 rpm

            Net

370 @ 2,800 rpm

      Horsepower/weight ratio

13.2:1

      Torque


            Gross

985 lb-ft @ 2,400 rpm

            Net

820 lb-ft @ 2,400 rpm

      Oil capacity

52 qt

Electrical system

24-volt

      Number of batteries

4

Transmission

cross-drive, CD-500-3

      Drive ranges

low, high, and reverse

      Range selector control box

mechanical

      Linkage to transmission

mechanical

      Torque converter

single-stage polyphase

      Gearshift and steering mechanism


            Internal

hydraulic

            External

mechanical

Fuel capacity

145 gal

Brakes


      Service

wet, multiple disk

      Parking

lock on service brake

Crew

4

Air transportability

--

Performance


      Maximum speed on level

to be determined

      Maximum grade climbing ability

to be determined

      Maximum trench crossing ability

72 in

      Height of obstacles that can be crossed

36 in

      Fording depth

48 in

      Turning radius

pivot

      Cruising range

to be determined