Gene, the hump is the area on the tripod head that the WW1 1917 traverse mechanism was housed. When they decided the 1918 tripod was a real pain to set up they redesigned the 1917 tripod, made the newer 1917a1 cradle, they eliminated the tripod head traverse. One of the problems of the 1917 was a lack of fine traverse which required training the gunners in a 2 finger tap of the rear of the cradle to finely adjust the cradle. Not precise in any way. This was at a time they were developing the indirect fire techniques pioneered by McBride of the Canadian Expeditionary forces. Which was the reason the army quickly shifted to the 1918 tripod which was a failure the soldiers hated.