Rotary OM is a narrow-gauge steam rotary snowplow built for the Denver & Rio Grande in 1889.
It was originally delivered as Rio Grande Rotary No. 1 and later received the maintenance-of-way designation OM.
Unlike a locomotive, a rotary plow’s steam machinery primarily powers the large cutting wheel at the front rather than propelling the vehicle along the track.
The rotary therefore requires one or more locomotives behind it to push the machine through snow.
OM was built during a period when heavy snowfall on mountain routes could block railroads faster than wedge plows and manual crews could reopen them.
The spinning wheel cut and threw snow away from the track, allowing railroads to attack deep drifts and hard-packed accumulations.
When Colorado and New Mexico purchased the Cumbres & Toltec route and equipment in 1970, OM survived as part of the inherited Rio Grande maintenance fleet.
The plow was used in preservation-era demonstrations during the 1970s after years of inactivity.
Later, the younger OY generally became the preferred rotary for major demonstration operations, while OM remained an exceptionally important preserved early rotary.
For TransitSatellite, OM should never be modeled or described as a self-propelled locomotive. Its route story must include the pushing locomotives, support cars, water, crew, and snow conditions that made rotary operation possible.