While researching WWI photographs at the US National Archives I found these two interesting photos. Captions for the photos are:
The French-built 75mm field gun used to fire the first US artillery shot against the Germans on 23 October 1917. According to the inscription on the blast shield, the gun was fired by Chief of Section, SGT Arch of South Bend, Indiana and Gunner CPL Bradley of Cincinnati, Ohio.
The French-made artillery piece, nicknamed "Calamity Jane," operated by a crew from the US 11th Artillery Brigade, that fired the last shot of the war for the Allies near Laneuville sur Meuse, France, November 11, 1918.
As I've posted here in Landships Modelling Forum (see http://www.landships.net/t60758847/gregs-french-75-mm-artillery-model/), I am scratch building a 1/8th scale model of the "First Shot" gun you mentioned. My grandfather, Lieutenant Harold M Hirsh, was in the AEF's Battery C of the 6th Field Artillery and participated* in that historic event. I remember reading his newspaper/magazine clippings about the historic event.
* He participated, but was not actually at the firing location when that first barrage was fired. After getting the guns in position, he and his men withdrew the Battery's horses to the "horse line" (a quieter, safer location some distance behind the firing line.)
Now I'm building the model in his honor. I hope to have it finished by the centennial of the actual event, but it's been very slow going. I've been working on the wooden/steel wheels for 3 months now. I'll post an update soon, when I actually have a wheel fully assembled.