In 1928, the Research Desk (OP-20-G) was planning to train US Navy radiomen how to intercept and exploit Imperial Japanese Navy (IJN) communications, which used a specialized telegraphic code based on the Japanese katakana syllabary. Unfortunately, the Main Navy Building on Constitution Avenue in Washington, DC was at capacity--there was no room to add a classroom for the planned training. Partly due to the space concerns and partly for security purposes, a steel-reinforced concrete blockhouse was built on the roof of the sixth wing of Main Navy Building to be used as a classroom for the new Radio Intelligence training.  Under the watchful eye of Chief Kidder, the classroom was designed to accommodate eight students and the radio intercept equipment necessary to conduct the training.  To get to class each day, the Radiomen in each course had to climb a ladder onto the roof.  The early classes began referring to themselves as “roofers” or “gumshoes.”