|SP 4462 with horn circled|
Steam locomotives used whistles and diesels use horns, right? Not entirely. As diesels began to replace steam locomotives, it became obvious that the steam-powered whistles that had been popular would have to be replaced with an air-powered horn. During this transition, there were some cases of horns being employed on steam locomotives.
The Southern Pacific used horns (in addition to whistles) on both the GS series 4-8-4s and the Cab-Forwards. The Cab-Forward had electric horns installed on the rear of their tenders. When Cab-Forwards were making a reverse move, it was difficult for the cab crew to see all the way to the rear of the tender. It was also difficult for a person standing near the rear of a Cab-Forward to hear the locomotive moving because they were so far away from the "noisy" part of the locomotive. A horn was used to alert anyone passing to the rear of the locomotive during these movements.