If he really was serving in an Ordnance Officer's billet at the time there is really just one likely location out of the few bases in Maryland. That being the Aberdeen Proving Ground just outside Baltimore. Built during WW1 the site was chosen as a replacement to the Sandy Hook Proving Ground in New Jersey as its smaller size and lack of more wide open space, and proximity to New York City made it less than ideal for testing ever more powerful artillery or chemical weapons. The base was and has been for a century now one of the homes of the US Army's Ordnance Corps, and weapons testing sites, along with housing and facilitating research for everything from new tank guns, to chemical warfare delivery weapons. It also provided a variety of terrain for testing new vehicles in development and was a storage depot for caches of chemical weapons though they have now been disposed of. Most relevant here it housed the Ordnance Center and School which would have run the various courses for US Officers and Enlisted that could have been attended by an Allied officer visiting for the purpose, though the Center has since been relocated to Fort Lee in Virginia.