They were designed for heavy freight work and were a development of the earlier 2800 Class. The 2884s differed from the original engines in a number of respects, the most obvious being that a more modern Collett side window cab was provided and that they were built with outside steam pipes.
83 of the 2884 class were built between 1938 and 1941. Those built during the war did not have the side window to the cab, and the side window on the others was plated over. This was to reduce glare, as a precaution against enemy air attacks.  The windows were reinstated after the war.
The locomotives were so popular with the ex-Great Western crews that the British Railways Western Region operating authorities wanted more of the class built after nationalisation in 1948; however, this request was turned down in favour of BR Standard Class 9Fs.
Between 1945 and 1947, coal shortages caused GWR to experiment with oil fired 2800 locomotives. Eight of the 2884 class were converted and renumbered from 4850. The experiment, encouraged by the government was abandoned in 1948 once the extra maintenance costs were calculated and the bill had arrived for the imported oil.
The year 1948 also saw one of the 2884 class, No.3803 (now preserved), emerge remarkably successfully from the 1948 Locomotive Exchange Trials against more modern engines including the LMS 8F and the WD Austerity 2-8-0 and WD Austerity 2-10-0. It took the appearance in 1954 of the British Railways BR standard class 9F 2-10-0 to displace the 2800s from their main role of mineral haulage. Nevertheless, there was still work for them right up to the end of steam on the Western region in 1965. Six decades of service testify to the fundamental excellence of Churchward's original conception.
No. 3863 on a down freight west of Patchway 12 August 1963