The Canal Zone Postal Service issued the 12-cent Canal Channel-After commemorative (Scott 129) of the Twenty-fifth Anniversary Series on August 15, 1939. The series includes eight 'before' and eight 'after' scenes of important Panama Canal areas and facilities.
The 12-cent stamp depicts the passenger/freight vessel SS Santa Clara on August 16, 1930, heading towards the Caribbean. The infamous Gold Hill (the origin of so many dangerous earth slides both during the construction era and after, the last significant one having occurred in 1986) in the background. The Santa Clara sails over the spot in the Canal channel where the pair of steam shovels featured on the 11-cent stamp met.
Like many of the stamps in this series, the 12-cent stamp had no specific use. Patrons might have applied it to a quadruple-weight domestic letter send by ship, but this type usage rarely appears. So, this value is almost always seen used with other stamps to make a rate — for instance, with a 3-cent stamp to pay the fifteen-cent airmail rate at the time.
Another of the stamps of this series that failed to sell out, the 12-cent stamp sold ca. 66,000 copies, and postal authorities destroyed over 143,000 on April 12, 1941.
Other than the numerous copies sold to collectors for retention or use on first day covers, very few of the 12-cent issue were used on non-philatelic mail. Even those found on mail from the Canal Zone Philatelic Agency rarely appear on cover.