Wall of text incoming, I'm sorry about this. However, I have been unable to find any pictures of the gun in question. In fact, either I am terrible at "teh Googlings," but after a brief search I can't seem to find a reference to this gun's existance online at all. Or in my Hunnicutt books. The idea of ten 37mm cannister rounds being fired at 90rpm has a certain appeal, though. The below does get a little technical, but it's an interesting insight into gun development.
I can either not share this information gleaned from one of my visits to the Archives due to the lack of pretty pictures, or, and I suspect that if you read the Hatch you're more interested in the data, I can put up a lot of words.
So, for those of you of stout constitution who want to learn about this little diversion the US Army played around with in WW2, fortify yourself, and read on!
In the Army’s discussion of the 37-mm Gun M6 it was noted that in August 1939 the Industrial Service of the Artillery Division revived interest in developing a breech mechanism for the 37-mm gun that would be completely automatic in opening and closing the breech and in feeding rounds into the gun. It was desirable to develop a gun which would require the least amount of space and servicing when mounted in a tank or airplane. One result of the recommendation for continued research and development on a fully automatic gun, was the semi-automatic 37-mm Gun M6 standardized in November 1940.
A project of research and development at Aberdeen Proving Ground was undertaken using as a basis the M6 gun. An automatic feed mechanism was designed and a rate of fire of between 90 and 100 shots per minute were obtained. A still higher rate of fire was felt possible with this gun and feed mechanism. The recoil mechanism of the M6 gun appeared to be limiting the rate of fire and work on a new type of hydro-spring recoil mechanism was undertaken.
The Ordnance Technical Committee approved the designation T16 for this experimental gun 23 October 1941. At the same time the manufacture of two recoil mechanisms was approved. One of these recoil mechanisms was to be used in the long recoil cylinder of the type on Mounts M19 and M20; the other was to be used in the short recoil cylinder of the type on Mounts M21, M22, and M24.
A counterrecoil spring was designed which surrounded the gun tube and which was contained in a housing on the sleigh. A valve governing the speed of counterrecoil was installed in a convenient location.
The 37-mm Gun Tl6 was a recoil operated, high velocity, automatic cannon, which weighed together with sleigh and recoil cylinder, 338 pounds.
The alloy steel gun tube, which had a bore length of 50 calibers, was screwed into an alloy steel breech ring and locked to it by a key and keyway. A drop-type breechblock, like that in the 37-mm Gun M6, was installed in the breech ring and was operated in the same manner.
To provide automatic fire and feeding a number of nonrecoiling assemblies were attached to the gun. These assemblies were the manual breech opening mechanism, trigger mechanism, loading mechanism, and the inclosing (sic) framework.
The breech of the gun could be opened manually by a handle located on the left side of the gun. Pulling this handle to the rear caused pressure on the rounded face of the closing spring mechanism and lever arm, and rotated the crank of the breechblock. Movement of the handle to the rear also held the loading tray up in position to receive a new round of ammunition. In its latched forward position, the handle, through linkage, released the loading tray.
The trigger mechanism of the T16 provided single shot or automatic fire. A knob and selector arm on the outside of the left side plate could be positioned for either of these methods of fire, or set in a "safe" position. In single shot fire a trigger guide, with the tripper pivoted on the rear end of the guide, moved rearward against spring pressure when the trigger was pulled. As the tripper moved rearward its curved forward arm was cammed against the rounded edge of the inner circular ring sector in the fire selector, rotating and moving rearward the beveled rear end of the tripper, and camming the trigger plunger inward against the sear to fire the gun. Further movement and rotation of the tripper carried the beveled end out of contact with the plunger and made it necessary to permit the mechanism to return to its original position before pulling the trigger again. With the selector arm set for automatic fire the gun would fire continuously as long as the trigger was held to the rear and rounds supplied. The fire selector, in this case, permitted the tripper guide and tripper to move rearward without rotation and cam the trigger plunger inward against the sear. When the gun returned to battery the left end of the trigger plunger again made contact with the end of the tripper and fired the gun.
The loading mechanism was located at the rear of the gun and was supported and pivoted on the left side plate. A tray, consisting of a perforated tube, was slotted to receive the round as it came from the feeding mechanism. The front end of the tray formed a sleeve through which the round was fed into the gun breech. The tray was attached to the rearward projecting arms of two levers pivoted on the left side plate. These arms were bent to position the tray on the vertical center line of the gun. A pin, attached to the rearmost arm, fitted behind the rim of the shell case and held the shell in place until the tray was lowered. The two levers supporting the tray were fastened at the ends of their short arms to a link so that they worked together as a unit. The front end of the link had a beveled lug to cam the catch rod to the right when the tray was lowered. A front and a rear slide guide were attached to the left side plate, each containing a flat rectangular plate which slid up and down in the guide. Protruding from each slide plate was an inward projecting, shouldered and flanged pin which engaged slotted holes in the long arms of the tvm levers mentioned above. The purpose of these slides and guides was to elevate the tray and control its movement. On the bottom of the front slide was an inward-projecting lug bearing on the outward-projecting lug of the lever arm. The front slide lug was beveled at the bottom rear to permit a slight lowering of the slide by the lug on the lever arm during recoil. A slide support was cammed beneath the front slide during the period of recoil when the lever arm and the slide lug lost contact. (1.15 inches from battery). When the lever arm, in counterrecoil, again engaged the slide support, it moved the support forward to allow the front slide to descend. The ammunition tray was moved to the lower or ramming position by a helical compression spring which was located in a housing and case attached on one end to the left side plate and on the other end to the link running between the two lever arms. This helical spring was compressed as the tray was raised to the upper position. Upon reaching the upper position the tray was held fast by a latch which projected into the rear sleeve of the tray from the rear housing. When a shell was fed into the tray the latch was struck and moved from the tray and the tray was lowered by action of the compressed springe As the tray was lowered to the ramming position, the front lug on the link cammed the catch rod to the right and moved the rammer latch out of engagement with the end of the rammer rod. The rammer head, rotated to its lower position behind the round by the descending tray, was carried forward by the action of its compressed spring and impelled the round from the tray into the gun chamber. As the rim of the shell made contact with the lips of the extractors on the breechblock the block was closed and the outward projecting lug on the lever arm elevated the front slide and the tray to their upper positions. This action compressed the spring of the tray mechanism. As the breechblock moved upward it rotated the rammer head to its upper position behind the breech ring. In recoiling, the rammer head was carried rearward by the breech ring and the rammer spring was compressed. After 16.5 inches of rearward travel, the rammer head was latched in the rear position by the spring actuated rammer latch engaging the end of the rammer rod.
During 1942 tests were conducted on the Tl6 Gun at the Aberdeen Proving Grounds. Before firing tests were begun two changes were made on the gun. The slide support and its components were replaced by a flat bar brazed to the left side of the closing spring housing. This was done to hold the front slide in the raised position while the gun was out of battery. The second change was the dampening of the motion of the ranmer rod and rammer head between the rear buffer position and the latched position. This was necessary because the rear surface of the rammer latch was being chipped.
A firing program of 125 rounds was carried out using a six round feed device. The first phase of the program consisted of firing 31 rounds of ammunition of mixed type (canister, the M63 HE Shell at 2,600 ft./sec. and the M51 APC Shot at both 2,900 ft./sec and 2,450 ft./sec.). This ammununition was fired in 5 round bursts at various elevations from -70° to +70°. In the second phase of the test 86 rounds of M63 shell (2,600 ft/sec.) and M51 shot (2,900 ft./sec.) were fired automatical.ly at the same ranges of elevation and depression. Seven rounds of the Practice Shell M55Al (2,600 ft./sec.) were fired at 0° elevation. One round of the Practice Shell M55Al was also fired at +70°.
The gun performed satisfactorily except for one misfire which occurred in each of the phases - both misfires were attributed to the firing pin guide. The lower lug was ground off the guide to permit the sear to release the guide with the minimum of friction. After this was done the gun functioned normally. On the one round fired at +70° elevation the rammer was not latched but the case was ejected.
On 21 October 1942 the Tank and Automotive Center, Detroit, requested Aberdeen Proving Ground to determine whether or not it would be practicable to install the Tl6 gun in the Light Tank M5. Aberdeen reported that it was impractical to do this without several modifications to the tank and to the gun. The modifications were of such a nature that complete redesign of some parts would be essential.
The trunnion brackets of the gun provided no means of attaching the gun shield. Changes in the mount were needed since the gun shield would not fit over the recoil and recuperator mechanism of the gun; the gun stabilizer could not be installed because the stabilizer mounting bracket would not fit over the rammer mechanism; the cartridge chute for the coaxial machine gun interfered with the rammer.
Three magazines were available for feeding this gun holding respectively one, five, and eight rounds. The five and eight round mechanisms presented interference on the right side of the gun which would eliminate the tank commander. The one round magazine actually provided three shots - one shot being contained in the gun, one in the tray, and one in the magazine. The Armored Force saw little advantage in this weapon as mounted in the Light Tank M5, since, with the M6 gun the time required for a stabilizer to return the gun to its original firing position allowed ample time for a good loader to have the gun ready for the next shot. Because of this unfavorable report the Tank and Automotive Center, Detroit, closed this project on 10 December 1942.
In February 1943 the Tl6 gun was subjected to a cold test at Aberdeen Proving Ground. The regular recoil oil was drained and Recoil Oil 2-36D placed in the recuperator. Fifteen rounds of Practice Shot M51 were fired in 5 round bursts at elevations of 0°, +45°, and -70° respectively. Alternate bursts of M51 shot-·and M63 shell were also fired at various elevations ranging from -70° to +70°. Following the removal of excess lubricant the gun functioned satisfactorily with the M51 shot. When firing the M63 shell at o0 elevation the recoil of 7 3/8 inches was too short to latch the rammer in the rear position. It was found that when two ounces of recoil oil were removed from the recuperator the gun would function normally. The average length of recoil was8 inches and the average cyclic rate was 89 r.p.m. No breakages were reported.
Functioning of the gun was satisfactory to the lowest test temperature of -23° F. when two ounces of recoil oil was removed from the recuperator. Normal functioning was obtained immediately without the firing of gun warming rounds.
Testing of the Tl6 gun in planes was carried on at Wright Field and revealed that this gun was not suitable for aircraft use without extensive modification.
Because further expenditure of funds on the Tl6 project was considered to be unwarranted, the project was cancelled in August 1944.