At the beginning of the thirties, the PLM in Algeria needed very powerful express locomotives, as the compound ten-wheelers used there had reached their limits, even when running in double. The specifications stipulated that the new locomotive alone should be able to pull trains with 19 to 29 cars sufficiently quickly over the ramps, which had often two percent, and should also have a maximum speed of 110 km/h or 68 mph. The result was a Garratt as a “Double Pacific” with 1.80 m (5 ft 11 in) driving wheels.
In 1932, a first prototype was built at Franco-Belge, which was tested first in France and then in Algeria. A special feature was the rotating coal bunker patented by Beyer-Peacock, which automatically transported the coal towards the cab. The cab was generously sized and had a fan to improve comfort in high temperatures. There were also controls in both directions and the Cossart valve gear was electrically actuated.
During the tests, up to 73 cars were successfully transported and the required speed was easily achieved with normal trains. The pulling power of the Garratt was now equated with the pulling power of 2.4 ten-wheelers. Only the special design of the coal bunker led to vibrations above 120 km/h, so it was no longer used in series production. The Kylchap exhaust system was replaced in the series by the usual double chimney of the PLM. The series locomotives were also given a streamlined casing.
After the 231-132 AT, twelve 231-132 BT were built in 1936, which reached up to 132 km/h (82 mph) and were therefore probably the fastest Garratts ever. On a better track, it was even expected that up to 140 km/h would be possible. When the first diesel locomotives were introduced after the Second World War, maintenance of the Garratts decreased. They were brought to Spain and scrapped at the beginning of the fifties.
