While the A1 was a fantastic locomotive that served its purpose as intended, it became clear reasonably quickly that some modifications could be made that would greatly improve its performance. These modifications however were too significant to avoid reclassifying the locomotives and as such the A1 Felstead 2743 was the first to be withdrawn from service only a handful of years after it was introduced, emerging from its shed in August 1928 as the first A3 ‘Super Pacific.’
The newly designated A3 locomotives had an improved boiler, larger cylinders and a conversion from right to left hand drive. 27 of the class were built as A3 locomotives from the get go, with all of the in service A1 examples being converted before 1950, the last such example to undergo this transformation was the then BR numbered 60068 Sir Visto.