Roger Hicks has written that Tri-X was introduced in about 1940 as a sheet film: the earliest references he had is a Kodak handbook dated 1940 and the BJ Almanac for 1941 (where it is reviewed as a new product and also advertised). Tri-X is mentioned in Dunn (Exposure Meters and Practical Exposure Control), 1952. The '50th anniversary' (2004) seemed to apply to roll film and 35mmm only but he had not found a date for this intro either. Web searches (including Kodak's own web site) give 1954 as the date of intro, but this is clearly not the case for sheet film.