Those people were probably part of a battalion heavy weapons company. Companies also had heavy weapons platoons. At one time the Army liked to put all their heavy machine guns in one unit and then parcel them out to infantry companies as needed. A company in the offense may not need them but a company defending would. I suppose the Army thought it was easier to train and maintain these personnel and weapons if they had them all together in one unit. Otherwise training might be hit and miss. When light machine-guns came along things changed.
From several pic's I have seen,the Army went to the metal machine gun cart about 1932. However,they still used the 1917 ammo cart and put a pintle on the rear cross-member to tow the machine gun cart. This reduced the number of mules by 1/2 and the machine gun crew went to 6-7 men. Got a similar pic of a 1932 WY NG unit with the gun carts hooked to the ammo carts and ready for march.
Finally found the unit ID for the photo - 11th Infantry, Company M. Regiment was stationed at Ft. Benjamin Harrison from 1922-1939 and I suspect that is the location for the photo based on the time period for the uniforms.
A forum community dedicated to Browning 1919 A4 firearm owners and enthusiasts. Come join the discussion about performance, gunsmithing, restoration, troubleshooting, reviews, accessories, classifieds, and more!