Need help with ID of 37-40mm AA gun and ammo used

Can anyone ID this gun and the ammo used for a museum?
My guess is circa 1920s-30s. Probably U.S. made, has vertical sliding wedge breech block. Probably single loaded, not belt or clip fed.
Large housing around the barrel has a large spring inside. Exposed portion of the barrel at the muzzle is knurled.

Is this for the 37 x 93mmR 1 pounder Hotchkiss, or the Navy Heavy 1 pounder cartridge, or perhaps something else?

Did not see anything similar in Bob Mellichamp’s superb book on 37mm Volume I that goes through 1913.

Can we get an image from the breech side?
Are any markings present?

Sorry, those are all I have to work from other than ones showing drawing/part numbers on a few parts
8074B and 4539B.

Hi all!

That’s our gun (I’m the guy who took the pics) and we’re baffled by it. It has a number of design elements from the Mk A 1-pdr, interwar US anti-aircraft sights on it and no data plate or manufacturer’s markings on it other than part numbers. The barrel is in full recoil position as you see it here (we elevated it shortly after and the entire barrel assembly fell out of the back of the gun!).

After exhaustive research by several of us here at the ADA Museum, our best guess is that it was a trials piece built in the 20s that was quickly overtaken by the Colt 37mm automatic gun, but any insight that anyone may have is GREATLY appreciated!


Jonathan Bernstein
US Army Air Defense Artillery Museum

Tony Williams- Any thoughts on this?
Bob Mellichamp- is this one in your books?
Jim Schoenung?
Gordon Spragge?

Someone out there knows something about this thing. Let’s help the Museum get a proper ID on it.

I’ve been scratching my head over this one.

My first thought was that this looks far too massive for a simple single-loader - it looks much more like an autoloader. But if there is no obvious provision for a clip, magazine or belt feed…

Is it possible to take any measurements of the inside of the chamber. In particular, the diameter of the open end, to give the maximum case diameter of the cartridge? Also, the check further into the chamber to see if there is a sudden reduction in diameter to indicate that the cartridge was bottlenecked (and, if so, the diameter of the case just before the bottleneck)? If we can identify the cartridge it fired we will at least be making progress!

Can we get photos from the e breech end, and also of the top of the breech/barrel area?

It will arrive here from Ft. Bliss next week and I will get measurements on it. It is definitely not an autoloader. The breech is similar in construction to the M1 37mm AT gun. I’ll post more pics next Wednesday as soon as I’ve got my hands on it.

Thanks all for your help!



Robert Mellichamp reports the following, and that it will be covered in Volume 3 of his 37mm Books.:

“The gun looks like a short barreled version of the American Armament corp antiaircraft gun M2 NO 1. This gun used a special case. I sold my last one to Bob Fenzel but occasionally I run into one in collections. The shell waa about equal to the MK III rounds used in the Browning M4 Aircraft gun (slightly higher velocity but not as good a projectile).The gun could be equipped with a automatic drum magazine or worked semiautomatically. The Dutch used a batch of these mounted on patrol boats in the East Indies during and after WW II. There are not too many around. I only know of single parts in the US. There may be one in an Australian museum along with a couple of NF& O CO 37 mm AT guns Bought by the Dutch. The U.S Army tested one mobile Auto gun verson at Watervliet Arsenal in 1939, but it was not adopted. It is rarer than the Schneider but they semed to have copied each other. circa 1938.”

Thanks so much for the help! The gun was supposed to get here from Bliss back in August, but due to some logistical screw ups, that never happened. It will be arriving next Wednesday 26 September and I will post pics of it thereafter.

Hello all!

The AAC M2 has finally arrived and we’ve re-attached the barrel (although it is still in full recoil). Here are the pics as it sits now: