Not normally interested in guns (Did I say that out aloud?)... but... couldn't help noticing that the gun had a shoulder rest like on the navy guns fitted to the tanks, is this normal for land artillery?
I did try to look it up... failed. But did find a nice site selling artillery of all ages. Sounded naff! but some interesting stuff on there. Cannon Superstore.
The second gun is indeed US designed and built - it's a Bethlehem Steel 37mm gun, the "semi-automatic" model. A handful were sold to France and were going to be used as anti-tank weapons, but apparently most were sent back to the US without ever being used. I think I've seen it referred to as the "M1918", but I wouldn't swear to it.
If you look closely you can see slots in the recoil mechanism, this may be one of the "cut-away instruction guns" mentioned by Robert Mellichamp in the latest volume of "A Gun For All Nations". The cut-away sections helped show the working parts, either to recruits being trained on the piece or perhaps to potential customers.
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“[B]ut these tanks are machines, their caterpillars run on as endless as the war, they are annihilation, they roll without feeling into the craters, and climb up again without stopping..." -Erich Maria Remarque