Twin 40mm Self-propelled Gun M42 in Easton, Pennsylvania.

This M42 features the three-prong flash suppressors on the 40mm guns, although they lack the reinforcing ring that was introduced late in the production run. The lineage of the 76mm gun tank M41 is obvious when looking at the lower hull and running gear. The stowage boxes over the fender were for 40mm ammunition, and two spare 40mm barrels were able to be stored under the left-side ammunition stowage boxes. One of the main engine air cleaners is mounted just behind the fender stowage box, and one of the main engine mufflers is at the rear of the fender.

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Twin 40mm Self-propelled Gun M42.

The turret interior and engine deck can be seen in this top-down view. This is an early machine with the conical flash hiders and the hinged hull roof doors between the drivers' doors. (Picture from TM 9-761A Self-propelled Twin 40-mm Gun T141.)

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Twin 40mm Self-propelled Gun M42.

The hull compartments are labeled in this drawing. The ammunition stowage compartment served as a base for the gun mount and also provided a tunnel on each side for interior stowage of a total of 192 40mm rounds packed in twelve 16-round cans. (Picture from FM 44-61 Procedures and Drills for Twin 40-mm Self-propelled Gun M42 and M42A1.)

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Twin 40mm Self-propelled Gun M42.

The interior layout is sketched in this cross-section. (Picture from TM 9-761A Self-propelled Twin 40-mm Gun T141.)

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Twin 40mm Self-propelled Gun M42 in Easton, Pennsylvania.

This detail of the turret front provides a better view of the three-prong flash suppressors that replaced the earlier conical flash hiders. The mount for the .30cal machine gun can be seen on the turret to the left of the picture, and peeking out from behind the gun shield to the right of the picture is the mount for the gunner's left-hand ring sight. Just above the lifting eyes on the gunner's shields are openings for radio antenna mounts.

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Twin 40mm Self-propelled Gun M42.

The radio antennas are shown mounted in this picture. (Picture from FM 44-61 Procedures and Drills for Twin 40-mm Self-propelled Gun M42 and M42A1.)

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Twin 40mm Self-propelled Gun M42 in Easton, Pennsylvania.

This side of the turret was home to the mount for the .30cal machine gun. The open-topped turret has been covered by now-rusty plate.

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Twin 40mm Self-propelled Gun M42 in Easton, Pennsylvania.

"Bam Bam's" front door is immediately obvious, with the hinge, spring, and hold-open latch on the right of the picture. The headlight mountings and guards are just outboard on both sides of the front door, and the driver's and commander's periscope guards are visible on top of their hatches.

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Twin 40mm Self-propelled Gun M42 in Easton, Pennsylvania.

This shot shows where two spare 40mm barrels were stowed under the fender stowage box. The fender itself is angled to a point like those on later-production M41 Walker Bulldogs.

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Twin 40mm Self-propelled Gun M42 at the Virginia Museum of Military Vehicles.

This vehicle has spare barrels stowed on the fender. The barrel could be changed in about 3 minutes.

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Twin 40mm Self-propelled Gun M42 at the Virginia Museum of Military Vehicles.

The extra barrels were stowed with their rear to the front of the vehicle. The recuperator springs can be seen around the end of the barrels.

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Twin 40mm Self-propelled Gun M42 at the Virginia Museum of Military Vehicles.

The mounting mechanism for the spare barrels is detailed in this image.

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Twin 40mm Self-propelled Gun M42 in Easton, Pennsylvania.

The vehicle commander occupied the seat in the hull front right, and the driver sat beside him. On early vehicles, the hull roof between the driver's and commander's hatches opened to the front and rear. This later-production vehicle does not feature these hull roof doors.

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Twin 40mm Self-propelled Gun M42.

The early overhead doors of the drivers' compartment are shown here in the open position. These allowed ammunition to easily be passed from the hull to the turret. (Picture from TM 9-761A Self-propelled Twin 40-mm Gun T141.)

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Twin 40mm Self-propelled Gun M42 in Easton, Pennsylvania.

Stowage boxes line the vehicle's right fender. Details of the suspension, including the volute spring bumper stops, can be seen at the bottom of the picture. The rear turret machine gun mount can also be seen at the very top of the photo.

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Twin 40mm Self-propelled Gun M42.

The stowage boxes are opened here. The front box contained retainers for a spare machine gun barrel as well as an oil can bracket, the latter of which can be seen at the lower front corner of the box. (Picture from TM 9-761A Self-propelled Twin 40-mm Gun T141.)

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Twin 40mm Self-propelled Gun M42.

Three ammunition stowage boxes were present on each side of the vehicle. The center boxes were interchangeable only with each other, while the other four boxes were all the same. Each of the boxes could stow ten 4-round clips, for a total of 240 rounds. (Picture from TM 9-761A Self-propelled Twin 40-mm Gun T141.)

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Twin 40mm Self-propelled Gun M42 in Easton, Pennsylvania.

This rear view shows the other main engine air cleaner. The right-side main engine muffler is just behind the air cleaner, and a better view is available of the rear machine gun mount and turret ammunition stowage boxes. A tool rack was normally placed on top of the right main engine muffler, but it is missing from this vehicle.

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Twin 40mm Self-propelled Gun M42.

An M60 machine gun has been mounted on the rear pintle here. (Picture from FM 44-61 Procedures and Drills for Twin 40-mm Self-propelled Gun M42 and M42A1.)

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Twin 40mm Self-propelled Gun M42 in Easton, Pennsylvania.

The shroud sitting just inboard of the main engine air cleaner was the exhaust port for the auxiliary engine. The pipe coming from the port indicates that this vehicle was equipped with a muffler for the auxiliary engine, but it has disappeared along with the tool rack on which it was mounted.

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Twin 40mm Self-propelled Gun M42 at the Virginia Museum of Military Vehicles.

The rear deck is better illustrated in this image. The air cleaners are behind the fender stowage boxes, and the engine compartment grille in the center of the rear deck is flanked to either side by two engine compartment grille doors. The plates in the center of the vehicle behind the engine grilles are the front and rear transmission access doors. These are flanked by the right and left battery access doors. The cover on the rear transmission access door is for the transmission oil filler, while the one on the front transmission access door is for engine oil. The gunner's speed ring sight for use with manual gun mount operation can be seen mounted to the turret to the gun shield's left.

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Twin 40mm Self-propelled Gun M42.

The engine compartment doors and grilles are labeled here. A 3.5" rocket launcher M20 could be stowed for self-defense. (Picture from TM 9-761A Self-propelled Twin 40-mm Gun T141.)

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Twin 40mm Self-propelled Gun M42.

The engine compartment is open in this picture, revealing the installation of the transmission. (Picture from TM 9-761A Self-propelled Twin 40-mm Gun T141.)

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Twin 40mm Self-propelled Gun M42.

The power pack has been removed here. (Picture from TM 9-761A Self-propelled Twin 40-mm Gun T141.)

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Twin 40mm Self-propelled Gun M42.

A schematic of the local control system M16A1E1 is given in this image. The oil gears drove the guns in elevation and azimuth. Electric motors drove oil pumps whose output, controlled by electric signals from the drive controller, went directly to the hydraulic motors which drove the gun mount. Components of the wiring set M10A1E1 included the inverter, which converted 24 volt direct current from the vehicle power supply to the 115 volt, 60 cycle, single phase, alternating current which controlled the output of the oil pumps; the distribution box, which contained terminal boards to which were connected the the 24 volt vehicle power supply, 115 volt inverter power supply, and telephone circuits; slip ring box, which fed the 24 volt vehicle power supply and telephone circuits from the hull to the gun mount via brush contacts; and the drive controller M12E2, which controlled the rate and direction of gun movement as well as firing of the guns via electrical triggers. (Picture from TM 9-761A Self-propelled Twin 40-mm Gun T141.)

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Twin 40mm Self-propelled Gun M42.

Some of the sighting and fire control equipment is labeled in this picture. The speed ring sights were for use when manually operating the gun mount, while the computer was for use with powered operation. The elevating speed ring was permanently mounted, and folded away when the reflex sight was used. The azimuth speed ring, on the other hand, was normally stowed in the sight case and this speed ring, peep sight, and holder were only assembled when needed. The speed rings were composed of seven concentric rings that were calibrated for the lead required for target speed of 100 to 700mph (160 to 1,100kph) in 100mph (160kph) increments. The twin 40mm gun mount M4E1 weighed around 6,300lb (2,900kg) complete with the gun. (Picture from TM 9-761A Self-propelled Twin 40-mm Gun T141.)

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Twin 40mm Self-propelled Gun M42 at Fort Knox, Kentucky.

The gunner's position is shown here, with his control handles in front of his seat. The left firing solenoid can be seen inboard of where his right shoulder would be positioned; just in front of this is the attachment base for the hand elevating crank, and the elevation oil gear is toward the front of the turret.

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Twin 40mm Self-propelled Gun M42.

Parts of the drive controller are labeled here. The fire control safety switch needed to be turned on before the triggers on the opposite side of the hand grips would work. (Picture from TM 9-761A Self-propelled Twin 40-mm Gun T141.)

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Twin 40mm Self-propelled Gun M42.

The manual elevation handcrank is shown here installed. The drive controller could be lowered out of the way when not needed; note the foot firing pedal that was used when operating in manual mode. (Picture from TM 9-761A Self-propelled Twin 40-mm Gun T141.)

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Twin 40mm Self-propelled Gun M42 at Fort Knox, Kentucky.

This is the sight setter's position opposite the gunner. The right firing solenoid can be seen near the position of his left shoulder, and ahead of him is the attachment for the hand traverse crank.

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Twin 40mm Self-propelled Gun M42.

The manual traverse handcrank is shown here installed; during manual operation the sight setter controlled the gun mount in traverse, while the gunner handled elevation and fired the guns via a mechanical foot pedal. (Picture from TM 9-761A Self-propelled Twin 40-mm Gun T141.)

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Twin 40mm Self-propelled Gun M42 at Fort Knox, Kentucky.

The computing sight M38 was mounted behind the sight setter's shield at the turret front.

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Twin 40mm Self-propelled Gun M42.

The computing sight mount was comprised of a support tube with the computer assembly on the right and the reflex sight support on the left. Handwheels were used to input the target's estimated course and speed, and the computer converted this data into leads for the guns. The results of the computations were transmitted through the housing assembly by motion of a telescoping shaft, which was resolved into drive bands which positioned the reflex sight with the proper amount of lead. The speed knobs were scaled from 0 to 700mph (0 to 1,100kph) in increments of 20mph (30kph). The angle of flight scale read from -85° to +60°. Azimuth, or angle of approach, was inputted by the computer positioning handwheel, which was graduated in increments of 800 mils. (Picture from TM 9-761A Self-propelled Twin 40-mm Gun T141.)

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Twin 40mm Self-propelled Gun M42.

The reflex sight M24C was able to be illuminated at night or in poor light via the light cable; the light's brightness was adjusted by the rheostat. Peep sights were provided to help with sight alignment with the target, and these could be swung out of the way when not in use. The crosshairs of the reflex sight were intended to be kept on the target, with adjustments being fed to the sight alignment via the target direction and speed data entered into the computing sight. (Picture from TM 9-761A Self-propelled Twin 40-mm Gun T141.)

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Twin 40mm Self-propelled Gun M42.

The reflex sight M24C is viewed from the left in this image. (Picture from TM 9-761A Self-propelled Twin 40-mm Gun T141.)

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Twin 40mm Self-propelled Gun M42 at the Virginia Museum of Military Vehicles.

Peering through the open front door, we are able to see the positions for the driver and commander. The personnel heater can be seen towards the center of the vehicle, and a heater duct snakes along the floor between the driver and commander.

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Twin 40mm Self-propelled Gun M42.

Three more 16-round 40mm ammunition cans could be strapped down between the driver and commander. (Picture from FM 44-61 Procedures and Drills for Twin 40-mm Self-propelled Gun M42 and M42A1.)

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Twin 40mm Self-propelled Gun M42.

Nomenclature of the various implements found in the driving compartment is given here. (Picture from TM 9-761A Self-propelled Twin 40-mm Gun T141.)

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Twin 40mm Self-propelled Gun M42 at the Virginia Museum of Military Vehicles.

The driver's position is detailed here. His steering control crossbar is placed directly in front of his seat, and his legs would reach around the vertical post to the foot pedals. The white transmission range selector control lever is placed in front of and to the right of the driver, and the black handle to the rear of the transmission range selector is the primer pump.

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Twin 40mm Self-propelled Gun M42 at the Virginia Museum of Military Vehicles.

The large perforated pedal is the accelerator, while the smaller pedal to its left is the brake. A cover for the front set of torsion bars can be seen running crosswise along the floor, and the mounting point for the idler wheel can be discerned on the hull side.

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Twin 40mm Self-propelled Gun M42 at the Virginia Museum of Military Vehicles.

The transmission range selector is detailed here. There are selections for reverse, low, high, neutral steer, and neutral park. The range selector was sprung so that it would return to neutral park from neutral steer once it was released; a neutral turn required holding the selector in position. Note the return springs attached to the brake pedal and the transmission range selector lever.

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Twin 40mm Self-propelled Gun M42 at the Virginia Museum of Military Vehicles.

The commander's position is shown here. Radio racks are provided to his right.

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Twin 40mm Self-propelled Gun M42 at the Virginia Museum of Military Vehicles.

The inside of the front door is illustrated here. Flashlight and periscope head stowage is labeled, and two interior locking handles are on the far end of the door.

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Twin 40mm Self-propelled Gun M42 at the Illinois State Military Museum.

The turret is reversed on this vehicle. It is a late-production machine equipped with features like the auxiliary engine muffler on the tool rack above the right main engine muffler and reinforcing rings around the flash suppressors. The auxiliary engine muffler is one of the second type fitted; earlier mufflers were smaller and did not extend the entire length of the tool rack. (Picture courtesy Kristopher Barrington.)

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Twin 40mm Self-propelled Gun M42 at the Virginia Museum of Military Vehicles.

A closer shot of the mounting of the auxiliary engine muffler and tool rack is provided here.

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Twin 40mm Self-propelled Gun M42.

The top covers of the 40mm guns are shown here, closed on the left and open on the right. The unmounted gun weighed around 2,000lb (900kg) without accessories, and the barrel assembly weighed around 296lb (134kg) each. The accuracy life was estimated to be 12,000 rounds, and each gun could average 120 rounds per minute of automatic fire. Up to 60 rounds could be fired in automatic mode before cooling was necessary. (Picture from TM 9-761A Self-propelled Twin 40-mm Gun T141.)

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Twin 40mm Self-propelled Gun M42.

The automatic loaders are shown here. They were fed from above by 4-round clips. (Picture from TM 9-761A Self-propelled Twin 40-mm Gun T141.)

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Twin 40mm Self-propelled Gun M42.

An exploded view of a breech ring is provided in this diagram. A. Loading tray bolt spring sleeve. B. Loading tray bolt spring. C. Loading tray bolt spring seat. D. Spring seat set screw. E. Safety plunger spring seat. F. Safety plunger spring. G. Breech ring safety plunger. H. Breech ring barrel catch. J. Flat-head screw. K. Breech ring barrel abutment. L. Barrel catch control arm. M. Extractor spindle. N. Extractor spindle arm. P. Breech ring crankshaft collar. Q. Right extractor. R. Left extractor. S. Crankshaft collar screw. T. Breech ring. (Picture from TM 9-761A Self-propelled Twin 40-mm Gun T141.)

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Twin 40mm Self-propelled Gun M42 at the US Army Heritage and Education Center at Carlisle Barracks.

A closer view of the flash suppressors with reinforcing rings is provided here.

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Last updated 2 Nov 2021.
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