A strike by union street car workers was under way in Kansas City, when the mayor called on the police department for assistance. Two hundred uniformed officers were assigned to guard duty, with reserves of officers and the 7th regiment on standby. Beginning on December 13, 1918, the officers were to function as guards for the crews and patrols with each car carrying two officers. Officers Frank Mansfield and George Stiver were assigned to street car #1119. Later that day the street car's air brakes failed as it traveled the Twelfth Street viaduct. The car jumped the track near Liberty Street and crashed into the Union Pacific Freight Building. Officer Stiver, who was riding at the front of the car, was uninjured. Officer Mansfield, who was at the rear of the car, suffered massive injuries in the crash. Two passengers died at the scene and many more were injured. Officer Mansfield was taken to General Hospital where he died of his injuries on December 16, 1918.

Officer Mansfield had been a member of the department only eight months when he was killed.