than an afternoon and erected in roughly six months. Wartime steel shortages forced the use of heavy wood timbers, and the Cambridge building authorities had to exempt the structure from city building codes. McCreery noted that Building 20 was designed and constructed "as a war measure, the life of said building to be for the duration of the war and six months thereafter."

In 1945, as the Rad Lab prepared to close down, these temporary buildings were not taken down immediately, since post-war student enrollments were increasing dramatically