Can anyone tell me which gun I am looking at?

German infantry waiting for the order to spring forward and go on the attack on the Eastern Front.

Waiting to attack

Heimat Pferdelazarett 12 Darmstadt
Beritt-R.A.D.

1. Reihe (first /  upper row , from left to right)
Ulrich, Walther ( my Great-Grandfather ), Räuchle, Bausch, Jörder, Funkner, Heckmann, Henrich, Herbig, Blau, Bartram, Schell, Fellmann, Steinmann

2.Reihe ( middle row )
Lutz, Simmet, Ritz, Knopf, Joseph, Albert, Derscheid, Gaul, Lammer, Schaaf, Pinger, Knopf Osk.

3. Reihe ( lower row )
Ott, Lupus, Vet.Dr. Göbel, D.-Vet.Dr. Lengler, D.-Stabsvet.Dr. Verbüchen, H.-Wachtmann Becker, Uffz. Brück, Uffz. Scherer, Uffz. Gahn, Doll