To eliminate the need for double-heading express trains, the FMSR ordered 20 Pacifics from Kitson, which were delivered in 1921. They had a superheated boiler with Belpaire firebox and were among the more powerful meter gauge Pacifics.
During World War II, the Japanese brought five of the locomotives to Burma, but they returned after the war ended. They soon became class 531 and some remained in service until 1971. The 531.01 was the only one that was preserved and is now in front of the National Museum in Kuala Lumpur. 