line drawing of a French 274 mm railway gun, probably Mle 1870/81
US War Department
Railway Artillery: A Report on the Characteristics, Scope of Utility, Etc., of Railway Artillery, Volume I, page 68, by Harry W Miller, United States Army Ordnance Department. Washington, Government Print Office, 1921. Downloaded from <a rel="nofollow" class="external free" href="https://archive.org/details/railwayartiller00deptgoog">https://archive.org/details/railwayartiller00deptgoog</a>