COL Zerbee's TD

The_Chieftain: 1. General This gun can be thought of as a conventional gun; the only difference is that it has no breech block. It is loaded with a cartridge containing an ignitor, a propelling charge and a projectile the same as any other gun. The difference is that the cartridge case is about four times as heavy as the projectile. It is usually the other way around. In the conventional gun the cartridge is fired at the breech while in this gun it is fired at the muzzle. In the conventional gun the recoil is transmitted to the breech block, thence to the carriage. In this gun there is no breech block and the energy of recoil is taken up in importing velocity to the cartridge case. At the moment of firing the velocity of the jeep forward is about equal to the velocity of the cartridge case aft. These two velocities balance each other and the velocity of the cartridge case with reference to the ground is nearly zero. Upon emerging from the breech it simply drops to the ground and does not endanger personnel by flying to the rear. The conventional gunaims to pierce armor by the velocity of its projectile. This gun, like a naval torpedo, aims to pierce armor by the violence of the detonation of its bursting charge. This is what I call the projectile a torpedo. At present each destroyer fires two torpedoes-one from each tube,and then withdraws to reload. But it appears entirely possible to fire three torpedoes from each without withdrawing to reload thus making the tank destroyer a six shooter.   1. Details of Construction and Suggestions for Improvement. The tank destroyer described herein was constructed from materials available at Fort Sam Houston and Camp Bullis, and withPost labor.   Chassis: The chassis is that of a Ford truck, Recon ½-ton, 4 x 4, a "jeep." with seats removed. The front springs have been reinforced with two extra leaves. The gas tank has been moved to the rear and the steering wheel has been lowered to decrease the silhouette. Suggestions for improvement: Some few members might be strengthened, particularly the tie rods between the front wheels.  Guns: Two pieces of old, rusty steam pipe, five inches internal diameter,1/4-inch thick, eleven feet long, and from the scrap heap at Camp Bullis. Suggestion for improvement: Much lighter pipe can be used, perhaps even 1/16 inch thick as there is almost no stress on it.  Gun Brackets: Two pieces of heavy angle iron, much better than necessary to carry the stress, from the junk heap at Camp Bullis. Suggestion for improvement: Lighter material  Cartridge Case: A World War four-inch Stokes mortar barrel turned down at the breech to fit into the guns. Suggestion for Improvement: A very much cheaper cartridge case can be produced.  Torpedo: A world war Four-inch stokes mortar bomb with an always fuze—loaded with about ten pounds of TNT. Suggestion for improvement: A very much thinner shell, one just strong enough to hold the fuze. It should contain no massive parts so as to minimize danger to friendly troops from flying fragments. Also, a thin shell will hold more TNT for the same total weight of filled shell.  Propellant: For TNT shell, about two ounces of black powder. Smokeless powder will not function in this gun. The pressure is too low. Grain size, the same as livens projector ignitor. For smoke shell sufficient of the same powder to get the range desired. The powder is enclosed for firing in a silk powder bag from a livens projector charge.  Ignitor: Commercial electric squibs. These are fired by commercial blasting machines through a series of safety switches. The squibs are placed in the propelling charge and the wires led out the muzzle of the cartridge case through grooves filed in the bourrelets of the torpedo.   Elevating Mechanism: None.  Traversing Mechanism: None. The driver aims the jeep itself. Suggestions for improvement: It would be quite possible to mount the guns on screw jacks if a means for varying elevation is decided upon, for smoke for instance. No traversing mechanism is recommended. The destroyer as it is now has proved itself sufficiently accurate in deflection.     Mechanically, the concept seems sound enough. It’s a recoilless weapon, and having a counter-mass is something which is in use today in some weapons. Despite some immediate thoughts of the wonder weapons that Dad’s Army may have come up with, especially given the construction materials, it’s not a bad idea. As far as actually hitting something is concerned, however, one must wonder about how this is expected unless the vehicle is driving on a large pool table or stationary on level ground. Still, the Army took a solid look at it. Probably since it was nearby, COL Montgomery of the Tank Destroyer Board took a drive down to check out a demonstration.  For the life of me, I can’t find the full copy of the report on my hard drive, though I could have sworn I had photographed it.  The gist of it, however, is as follows:  The test started the the TD in a concealed position some 800-1,000 yards from the target, a tank silhouette. The vehicle then attacked the target by starting toward it at maximum practicable rate of speed, the vehicle being pointed directly toward the target. At about 100 yards distant, the driver-gunner fired, and after firing, the vehicle veered away from the target.  Although the first part of the run was of fairly rough terrain, the last 200-300 yards was on level and fairly smooth ground surface, which favoured the “aim” in both direction and range. Some experimenting was done in the loading of the black powder charge to vary the velocity and trajectory.  Results in hitting the silhouette target by the dummy projectiles used was not favourable to the weapon. Out of nine trials where conditions were acceptable for test purposes, only two hits resulted.  The vehicle and firing tube were in no way affected by the charge. This was to be expected since the firing tube was not subjected to pressure.  The assessment continued:  The conditions under which the demonstration was conducted were highly special in that the ground about the target was level and smooth. Had the ground, on the contrary, been rough, the possibility of a hit with a projectile launching device which cannot be aimed independent of the stance of the vehicle at instant of firing must be regarded as remote.  The mounting of a launcher of any kind on a vehicle which is to fire in motion must be free so that the launcher can be pointed independently of the moving vehicle whose position at the instant of firing is affected by the terrain. In the combat vehicle demonstrated, the launchers are rigidly attached to the vehicle. If the target were fixed and the weapon-carrying vehicle similar to the one tested could select a particular route of approach so that at the right distance from the target, the direction of the vehicle, the slope of the ground, and the degree of deflection of the springs could be all shown, hits could doubtless be had, but such a set-up cannot be expected in combat.  Col Zerbee apparently thought about this a little bit, and concluded that a solution would be to load up a couple more tubes, and fire a 14-round burst, relying on dispersion of a number of rounds to obtain at least one hit. I am reminded somewhat of the Hedgehog or RBU anti-submarine weapons. The official conclusion of the report was  The weapon in its present form cannot be advantageously employed againsttt   tanks for the   reason that it cannot be dependably aimed at targets of comparatively limited size. Colonel Zerbee’s answer to this question is not considered a dependable solution to the problem of accurate aiming of his weapon.  The end result was that the creativity shown by Col Zerbee’s thought-out solution was appreciated, even if it was perhaps a little optimistic. Of course, the issue of equipping jeeps with recoilless rifles was more or less solved by giving guys in a jeep a bazooka. The overall concept, incidentally, reminds me of the Grenadier Tank Destroyer Battalion I covered earlier.  As ever, my Facebook page remains here, my Youtube channel here, and Twitch stream (Every Tuesday, and occasional evenings) is here.