No, it means that they (the gunmen and the armored car) opened fire/started firing at the tail of a convoy east of Hartennes.It means that their convoy was shot at by cavalry machineguns and armored car east of Hartennes?Les mitrailleurs de cavalerie, et l'auto mitrailleuse ouvrent le feu sur la queue d'un convoi à l'Est d'Hartennes
I think that the word I couldn't read didn't hinder understanding of the fragment:Vers 9h les Btns sont embarqués en autobus et suivent l'itinéraire Hartennes - Cramaille - Maroeul en Dole -Chery- Chaque Bataillon est affecté à une Division de Cavalerie
"About 9am, the battalions are embarked on autobuses and follow the route [names of the Places] Each battalion is attached to one cavalry division"
I don't know if "follow the route" is a perfect translation for "suivre l'itinéraire" but I guess it gets the meaning across.
"Maroeul-en-Dôle" appears as "Mareuil-en-Dôle" on maps today. I don't know if this is bacause the spelling was different back then (pronunciation would be the same) or because the writer made a mistake.