In the middle 1950s, the engineering staff of the Montreal Terminal proposed a radical new style of steam engine so that the MTRR could continue to economically operate steam. What they proposed was a steam engine that was fairly common in Europe, Asia, and Africa, but completely unknown in North America: a Beyer-Garratt double mikado.
20 used a custom-built water-tube boiler, a main frame built by the PV&T shops, and the engine frames from retired mikados 201 and 207. When it was put into operation in 1958, it was quite successful; it was 20% more fuel efficient than the mikados were, it had much better tractive effort when fully fueled (Beyer-Garratt locomotives traditionally carried water and fuel on their locomotive chassis, which meant that tractive effort fell off as the locomotive operated), and it was, after some initial balking, universally loved by the train crews. The only weak point was the water-tube boiler, which, like every other water-tube boiler used in North American railway service, leaked like a sieve after being in service for six months. The boiler was then replaced with the boiler off #17, and the GA prototype became the best loved engine on the MTRR.
In 1960, the MTRR proposed to build a small fleet of GAs to replace most of the wearier road locomotives in service. Alas, this was not to happen; the PV&T + LT&L + MTRR merger was in process, and the PV&T preferred to use diesels on their nonelectrified lines, so in 1962 20 was cocooned and placed into storage, where it remains today.