AirChime traces its beginnings through the work of Robert Swanson in 1949. Prior to the early 1950s, locomotives were equipped with air horns that sounded a singular note. Swanson sought to develop an air horn that would mimic the sound of a classic steam whistle. Using ancient Chinese musical theory, Swanson produced the six-note model H6. This was impractical for railroad use, however, due to its relatively large size. Railroad equipment operates over routes restricted by loading gauge, and a difference of only a few inches may prohibit that equipment from operating on the line in question.
Swanson would later refine the H6 with the model H5. As the numeric designation indicates, the horn sounds a five-note chord. In 1950, AirChime introduced its M series, a further improvement on the earlier horns by the elimination of unnecessary moving parts. Among the earliest customers of the AirChime M was the Southern Railway, which sought replacement horns for their motive power.
Under Swanson’s guidance, AirChime focused on ease of mass production, low maintenance, and reliability in their air horn design, with the development of the P (1953) and K (1954) series. AirChime was subsequently sold to its American licensee, Nathan Manufacturing, Inc., a division of Micro Precision Group, Inc. in Windham, Connecticut.