RECOILLESS WEAPONS RIFLE, 57-MM, T15E13 and T15E9 RIFLE, 75-MM, T21 HOWITZER, 105-MM, T9 and CARRIAGE, T9 OFFICE OF THE CHIEF OF ORDNANCE WASHINGTON, D.C. FEBRUARY 1945

WHILE the necessity of providing our troops with superior fire power has long been recognized, experience in this war has sharply emphasized this principle. Warfare today is not static warfare of position, with great armies confronting each other along well defined lines and relatively small fronts; rather it is fluid warfare, a swiftly changing panorama of break-throughs, airborne and beach-head actions, and frequent isolated engagements. Hence the need for highly mobile and portable weapons quickly became apparent and has resulted in such successful developments as the rifle grenade, the shoulder fired rocket launcher, mortars and similar light weapons. As the urgency for improved accuracy and increased range in weapons of this type grew apace, the Ordnance Department initiated projects to provide equipment capable of firing high explosive shell with these characteristics, yet light enough to accompany infantry in almost every tactical operation.

A controlling factor in weapon design has always been that of weight, and weight is inevitably largely determined by the phenomenon of recoil. As recoil increases so must the weight of compensating mechanisms or support increase. To produce equipment that would possess the desired characteristics several weapons have been designed in which recoil has been eliminated. This has been accomplished by balancing the forward and rearward momentum that occurs in firing—the simplest and most efficient method.

The elimination of recoil and consequent heavy carriages has meant that these weapons are extremely light; that they can be produced rapidly and economically and that they can be readily shipped, an important consideration when supply lines cross oceans.

The recoilless rifles and howitzer presented in this booklet have been produced to provide infantry with assault weapons comparable to artillery. Their light weight, simple design, and ease of handling indicate employment in a great many tactical situations heretofore unsupported by superior firepower.

THE 57-mm rifles, T15E13 and T15E9, operating on the recoilless principle, have been designed to provide an antipersonnel and antitank weapon of lighter weight and greater range and accuracy than other comparable light weight weapons.

This rifle operates on principles similar to those of a conventional gun except in the characteristics of the breech. Upon ignition of the propelling charge, a controlled amount of gas is allowed to escape to the rear, which, with the forward momentum of the shell, creates equal and opposing forces within the rifle. The force exerted by the projectile in its forward passage through the tube counteracts the force of the gas escaping through Venturi openings in the breech. Hence, since these two forces are balanced, the rifle does not move appreciably. Moreover, the Venturi openings are designed to exert a rotational reaction which offsets the torque induced in the rifle by the movement of the projectile through the rifling.

The cartridge case of the round for this rifle is smaller in diameter than the interior of the chamber; it is perforated to allow radial escape of gas into the chamber and thence to the rear until controlled by the Venturi openings. The round as thus proportioned is compact and easily transported.

The rifles T15E9 and E13 differ only in the rifling of the tube. The rifling in the T15E9 is one turn in 25 calibers and in the T15E13, one in 30 calibers.

Extendable Front Handle T3E1 and Bipod T3E1 are provided. The latter, when folded, becomes a shoulder rest, permitting the rifle to be fired from the shoulder in standing, sitting or kneeling positions. The front handle may be extended and the bipod unfolded to furnish three point support for prone firing. The rifle may also be mounted on the cal. .30 Machine Gun Tripod. Front Sight, T91 and Sight Mount, T120E2, provide attached iron sights, the rear sight leaf being similar to the cal. .30, M1903 rifle. Telescope Sight T130E2 may be quickly attached to the Sight Mount T120E2.

On Mount, Tripod, Cal. .30, M1917A1

Bipod, T3E1, Folded for Firing from Shoulder

CHARACTERISTICS
RIFLE, 57-MM, T15E13
Weight (gun complete—for mounting on tripod)		40.25 lb.
Length, over-all		60 in.
Recoil mechanism		None, recoilless
Muzzle velocity		1,200 f/s
Maximum range		4,400 yd. with Shell, H.E., 57-mm, T22
Type of breechblock		Interrupted lug
Firing mechanism		Spring loaded hammer, floating firing pin, trigger operated sear
Rifling		1 turn in 30 calibers—uniform, right hand
Mount		Bipod, T3E1 forms rest for shoulder firing or bipod for prone firing used in conjunction with extendable front Handle, T3E1
Alternate Mount		Mount, Tripod, Cal. .30, M1917A1
Iron Sights		Sight, Front, T91 and Mount, Sight, T120E2 provide iron sights when telescope is not used
Telescopic sight		Direct Fire Telescope, T130E2
Elevation (on Mount, Tripod, Cal. .30, M1917A1)		+65°
Depression (on Mount, Tripod, Cal. .30, M1917A1)		-27°
Traverse (on Mount, Tripod, Cal. .30, M1917A1)		360°
Height—in firing position
(on Mount, Tripod, Cal. .30, M1917A1)		0° elevation 34¼ in. to top of breechblock handle
Width—in Firing position		12 in. (gun and sight mounting bracket only)
ACCESSORIES
1. Cover, T27E2
2. Cover, T38 (Muzzle and Breech)
3. Bag, Canvas, Rocket, M6 (for transporting ammunition)
4. Packboard, Plywood & straps w/ buckles, quick-release & attachments, cargo
5. Mount, Tripod, Cal. .30, M1917A1

Firing from Standing Position

Firing from Kneeling Position

Firing from Prone Position

Carried on Packboard, in Cover, T27E2

Carried by Two Men in Cover, T27E2, with Slings. Three Rounds Carried in Bag, Canvas, Rocket, M6

The H.E. Shell, T22, was developed to provide a high explosive, antipersonnel round for the 57-mm recoilless rifle. This round is provided with a point detonating fuze, T119E1.

The H.E.A.T. Shell, T20E2, was developed to provide a round for use against armored vehicles. It is provided with a point initiating fuze, T123E1, and has penetrated homogeneous armor plate up to 3 inches at 20° obliquity.

The WP Shell, T23, was developed to provide a round for smoke screening, antipersonnel effect, and for spotting. The T119E1 fuze is used with this round.

All of these rounds use a perforated steel cartridge case instead of the usual solid case. The case has a paper liner which retains the propellant charge and bursts upon ignition, allowing the release of gases through Venturi tubes in the rear of the gun. All shell have pre-engraved rotating bands in order to reduce the amount of pressure required to expel the shell from the rifle.

CHARACTERISTICS

Shell

Shell & Fuze Weight

Fuze Type

Primer

Cartridge Case

w/o

Complete Rd. Weight w/ container

H.E., 57-mm, T22

2.75 lb.

P.D.

Perc., T37

Steel, T1

5.30

7.12 lb.

H.E.A.T., 57-mm, T20E2

2.75 lb.

P.I.

Perc., T37

Steel, T1

5.30

7.12 lb.

Smoke (WP), 57-mm, T23

2.75 lb.

P.D.

Perc., T37

Steel, T1

5.30

7.12 lb.

Cartridge, H.E., 57-mm, T22

THE 75-MM Rifle T21 has also been designed as an antitank and antipersonnel weapon with a range and fire power comparable to a howitzer, the accuracy of small arms, and yet light enough to accompany infantry.

The T21 Rifle operates on the same principles as the 57-mm recoilless rifle and fires, at normal velocity of 1,000 f/s, a standard 75-mm H.E.A.T. projectile with pre-engraved rotating band and other slight modifications. Similarly modified standard H.E. and WP projectiles are also fired at the above velocity.

Weighing but 105 pounds this rifle may be carried short distances by 2 to 4 men. It is quickly and easily mounted on the cal. .30, M1917A1 Tripod Mount. Provided the range is not too great it may be used for supporting artillery fire. Maximum range is approximately 7,000 yards.

Although the T21 Rifle is primarily a direct fire weapon, an elevation quadrant, and leveling jacks to bring the pintle into a level plane, are provided.

Paracrates to allow the rifle to be dropped from airplanes are under development and it is anticipated that it will become an important addition to the equipment of airborne troops.

CHARACTERISTICS
Weight (gun w/o sights or tripod)		105 lb.
Length, over-all		81.78 in.
Recoil mechanism		None, recoilless
Muzzle velocity		1,000 f/s
Type of breechblock		Interrupted lug
Firing mechanism		Spring loaded hammer, floating firing pin, trigger operated sear
Rifling		1 turn in 22 calibers—uniform, right hand
Elevation (on Mount, Tripod, caliber .30, M1917A1)		+65°
Depression (on Mount, Tripod, caliber .30, M1917A1)		-27°
Traverse (on Mount, Tripod, caliber .30, M1917A1)		360°
ACCESSORIES
1. Mount, Tripod, M1917A1
2. Jacks, Leveling, T1
3. Cover, T39 (Muzzle & Breech)
OPTICAL FIRE CONTROL EQUIPMENT
Telescope, T126E2
Quadrant, Elevation, T13E1

Breechblock in Open Position

Shell similar to those for the 57-mm rifle were developed for the 75-mm T21 Rifle. The Shell, H.E., 75-mm, T38, is an antipersonnel round, and the Shell, H.E.A.T., T39, an antitank round which will penetrate homogeneous armor plate to a depth of 4 to 4.5 inches at all ranges and at all obliquities from 0° to 60°.

The WP shell T23 will be used for smoke screening, antipersonnel effect and for spotting.

The H.E. shell uses the point detonating fuze M48A2, the H.E.A.T., the base detonating fuze M62, A1, and the WP shell, the point detonating M57 fuze.

These rounds also use a perforated steel cartridge case and have pre-engraved rotating bands.

CHARACTERISTICS
Shell		Shell & Fuze Weight		Fuze Type		Primer		Cartridge Case		Complete Rd. Weight
H.E., 75-mm, T38		14.4 lb.		P.D.		M28A2		Steel, T7		21.85 lb.
H.E.A.T., 75-mm, T39		13.08 lb.		B.D.		M28A2		Steel, T7		20.44 lb.
Smoke (WP), 75-mm, T40		15.1 lb.		P.D.		M28A2		Steel, T7		22.61 lb.

Cartridge, H.E., 75-mm, T38

HOWITZER, 105-mm, T9 and CARRIAGE, T9 in traveling position behind 1/4 ton 4x4 truck

HOWITZER T9, in firing position

THE Recoilless Howitzer T9 has been developed to provide an artillery weapon combining adequate fire power with extremely light weight for use over difficult terrain and by airborne troops. It fires the same shell as the 105-mm Howitzer, M3, and M2A1.

The absence of recoil in the specially constructed howitzer permits the use of an exceptionally light carriage. The rearward movement of the gases through the nozzle balances the forward movement of the projectile. The breechblock which carries the nozzle is of the horizontal sliding block type and the removable breech ring is locked to the tube with interrupted collars. The equilibrator and elevating mechanism are combined in a single unit consisting of two tubes containing both spring and screw elevating jacks connecting the top carriage to the front of the breech ring.

When in firing position, the carriage is supported on three trails which fold up and lock to the tube to form a rigid mount in the traveling position. The wheels are readily removable for emplacement, if desired.

The T9 Howitzer and Carriage have been designed to be readily disassembled into loads suitable for paracrates or pack transports. None of the loads exceed 200 pounds.

The weight of the howitzer and carriage is approximately 750 pounds while the weight of a similar German recoilless howitzer, 10.5 cm. L.G. 12 with shield, is reported as 1,217 pounds.

It is anticipated that all standard shell now fired in 105-mm howitzers will be satisfactory for use in the T9. The cartridge case, which has a plastic blow-out plug in the base, has a capacity of approximately 300 cubic inches. Due to its larger diameter there is no likelihood of its being mistaken for regular 105-mm ammunition.

Initial firing tests to date indicate that velocities of approximately 1,050 f/s with the 105-mm Shell, H.E., M1, are obtained with granular powder, within the pressure limits of the T9 Howitzer. Range is approximately 7,500 yards. The ammunition is semi-fixed and the complete round will weigh approximately 51.5 pounds.

The fragments of the plastic blow-out plug in the base of the cartridge case, the rearward flash of the propellant, and the dust and stones picked up by the gases creates an unsafe area directly in back of the howitzer for about 100 yards. Safety restrictions will be determined.

Complete Round for Howitzer, 105-mm, T9           Three-quarters Rear View Showing Plastic Blow-Out Plug

CHARACTERISTICS
HOWITZER, 105-MM, T9
Weight		415 lb.
Length, over-all		88.73 in.
Length of bore		15.99 cal.
Rifling		Uniform, right hand, 1 turn in 20 cal.
Firing mechanism		Trip off
Chamber capacity		300 cu. in.
Muzzle velocity		1,050 f/s approx.
Maximum range		7,500 yd. approx.
CARRIAGE, T9
Weight		335 lb.
Traverse		80° (total)
Elevation		-5° to +65°
Tread width		48 in. (est.)
Time to emplace		1 min.
Road clearance		6 3/8 in.
Height
Traveling		43 3/4 in.
Firing		46 3/4 in.
Width
Traveling		57 in.
Firing		72 in.
SIGHTING AND FIRE CONTROL EQUIPMENT
1. Telescope, Elbow, M62
2. Mount, Telescope, T93
3. Adapter, Telescope, M9