British Commonwealth Air Training Plan
Created as a result of an agreement signed by the United Kingdom and Canada on 17 December, 1939 this Plan was one of Canada's most important contributions to the Allied war effort in World War II. Over 130,000 airmen from the forces of the Commonwealth and other countries, including pilots, navigators, bomb aimers, wireless operators and gunners, trained at schools established across Canada. Many of the instructors who were the mainstay of the Plan came from the Trenton base. Airfields built for the Plan became part of Canada's postwar aviation network.
Plaque via Alan L. Brown's site Ontario Plaques. Full page here.