Until the Guns Come Off the Line…

An article written by Capt. Howard R. Johnson detailing how to build a replica of an anti-tank gun appeared in "Until The Guns Come Off The Line," in the November-December 1940 Infantry Journal. No, Capt. Johnson had not finished his jeep and needed new toys. Actually this was written before most units had ever seen or heard of the jeep. Using his skill and creativity, Captain Johnson developed a training device during a time when equipment shortage was at its peak.
Figure 1. Mac McCluskey's complete 37 mm Anti-Tank Gun replica behind his WWII jeep. BDMP BrooksDigital.com
The American military was building and preparing for war. The strength of the US Army consisted of 620,774 officers and enlisted men as of December 31, 1940. The size of the Army doubled six months later to 1,460,998. Doubling the size of the Army generated many problems including shortages of equipment. After decades of neglect during the inter-war period, the Army was finally being re-equipped but "until the guns came off the line" demands could not be met. Capt. Johnson and his men needed equipment on which to train. The solution was to build "guns" locally for training purposes.
Figure 2. An example of both the quality of the drawings made from the original micro-film and the information contained on each drawing necessary for a machinist to build the part. Mac McCluskey collection Johnson procured the remains of Dodge trucks from the local military vehicle dump. The rear axles were pulled and used as a platform on which to mount a pipe barrel and "armored" shielding. The replica gun was used for loading practice by the crew. The crew could practice the motions required to load and fire the weapon. Captain Johnson recommended that at least one real 37mm anti-tank gun be made available per company of men.A REPLICA FOR COLLECTORS

Once you have your jeep or other light military 4x4 vehicle restored or completed to your satisfaction the question becomes, "Do you move onto other vehicles or collect other toys?"

Collectors can build the AT gun for other reasons and it is sure to get you some interesting looks! After offering Captain Johnson's original WWII article on the Internet site, G503.com, several of forum members began to coordinate the design and building of a new, more accurate "training" device loosely based on Captain Johnson's article.

Figure 3. The completed part, the shoulder guard as produced by Mac and fully installed. BDMP BrooksDigital.com

One of the modern-day developers, Mac McCluskey, a machinist by trade, stumbled upon a gold mine of information during a military vehicle show on the West Coast. He met a fellow enthusiast and during the ensuing discussion about "jeeps" and military vehicles, the subject of the 37mm anti-tank gun came up. Turns out, the man had the a complete set of ordnance drawings for the gun...would Mac be interested in those? You bet! Who would not want to pull such a piece of "art" behind their WWII jeep?

The drawings had been printed from microfilm so they were not perfect, but Mac knew how to read the prints and could build the parts. After review of the drawings, Mac led off with the production of some basic parts. What follows is the photographic display of his M3A1 37mm Anti-Tank Gun (Training) and M4A1 Carriage. The detail of his work is nothing short of amazing.

Figure 4. Two cast pieces ready to be machined and then welded together to form the breech. Note the superb quality of his workmanship as evidenced by the two hand-wheels. BDMP BrooksDigital.com

The breech of the gun was fabricated by Mac from a two piece casting created by Lee Hoskins. Mac machined the pieces separately then welded them together. Of course, for a fully functional weapon, the piece would have needed to be made from a single cast piece and of hardened steel. Mac was only interested in building a non-firing replica.

After the breech was welded together, the breech ring needed to be machined so that the barrel would fit. There are still several steps to go for preparing the breech. Once the remaining steps were completed the breech and breech block were fitted to the barrel.

The original anti-tank gun sported a scope for zeroing in on Axis tanks. Mac was able to use a rifle scope purchased from a local shop to simulate the original piece.

Figure 5. Mac purchased a rifle scope from a local shop to fill in as a 37mm spotting scope. The leather case to the left is the stowage location for the scope. BDMP BrooksDigital.com

There were traverse and elevation wheels on the gun. When the operator changed the elevation of the barrel the same action changed the elevation of the scope. The leather case is for stowage of the spotting scope when traveling.

Towing the gun required a ring so that a standard pintle hook could be used. The ring could be rotated to adjust the height of the travails so that the spades would not dig into the earth when towing.

Figure 6. The 37mm anti-tank gun ready for towing. Further evidence to Mac's skill as a machinist are evident in his recreation of the "goose-neck" towing ring that can be adjusted to varying heights like the original. BDMP BrooksDigital.com

At first, the segment spokes look like part of the fenders. This is actually the "segment wheel" in the traveling position. When the gun was prepared for use, the segment wheels were reversed and actually lifted the wheels off the ground. This helped to keep the weapon from moving (along with the spades) when fired.

Figure 7. Over the wheel there appears to be a fender of sorts--this is actually the segment wheel. The segment wheel is rotated toward the ground. When the gun is in the firing position the carriage rests on the segment wheels which reduces recoil movement (along with the spades). BDMP BrooksDigital.com

The business end of the weapon illustrates many complex pieces that had to be fabricated by Mac. The barrel was made from several pieces which had to be machined to exacting tolerances in order to replicate an original barrel. Below the barrel is the recoil mechanism.

Figure 8. Close-up view of the segment wheel in the "firing" position. BDMP BrooksDigital.com

The tires used on the replica are non-directional tires (NDT), however, the original weapon would have had regular automobile "street" tires. Still, the NDTs look good on the gun.

Figure 9. This photo illustrates the complexity of the gun, almost all of which was fabricated by Mac. This included the gun barrel, recoil mechanism, axle, traversing gearing, segmented wheels, etc. BDMP BrooksDigital.com

It took Mac a approximately two years to complete the replica of the 37mm Anti-Tank Gun. But as the last photo illustrates, it is a fine example of what an expert machinist can do.

Figure 10. The travails moved outward to the "firing" position and ready to be served by the gun crew. BDMP BrooksDigital.com