Many sources claim origin as early as 1939.[2][6][7] An early example of the phrase may date from 1937, before World War II. The US History Channel broadcast Fort Knox: Secrets Revealed in 2007 included a shot of a chalked "KILROY WAS HERE" dated 1937-05-13. Fort Knox's vault was loaded in 1937 and inaccessible until the 1970s, when an audit was carried out and the footage was shot.[8] However, historian Paul Urbahns was involved in the production of the program, and he says that the footage was a reconstruction.[9]