Forward to 1903 and the SECR with Wainwright in charge. Wainwright set out to rebuild the "F Class" and thereby prolong their useful life and did such a good job that some would see service into early BR days. The "F Class" boilers had no dome over the safety valves, nor much of a cab to protect the crew in inclement weather. The rebuilt "F1 Class" had both a domed boiler whose centre was raised from the F's 7' 5" to 7' 10" (with Ramsbottom safety valves fitted on the firebox) and increased pressure which was up from 160 lb per sq in to 170. A larger cab was provided which was, in fact, similar to that fitted to Stirling's B Class engines. Minor modification to the smokebox front left the engines looking identical to the subsequent B1 Class of 1910, in fact the only way to tell the two classes apart is from looking at their tenders, the F1s having prominent outside springs! In all, some 76 of the 88 "F Class" were rebuilt as class F1.

The final twist in the F1 story came during WWII when nine of the class were lent to the LMS, where they were classified as 2P. This arrangement lasted from 1941 until the last was returned in mid-September 1944.