They were a development by Frederick Hawksworth of Charles Collett's earlier Hall Class named after English and Welsh country houses.

Hawksworth decided that the declining quality of coal reaching Great Western depots necessitated a higher degree of superheating.

The first batch of twelve Modified Halls was delivered from Swindon works between March and September 1944.

They carried plain black livery, were unnamed and numbered 6959-6970 (immediately following the Hall Class sequence).

[citation needed] A further batch of ten locomotives appeared during October and November 1947 and others were on order when the nationalisation of Britain's railways took place in 1948.

The Modified Hall class 'ran freely, steamed well and were popular with both footplate and maintenance staff.

[citation needed] 6998 was a popular mainline performer in the late 1980s, and also in the 1990s, until 1996 when she was withdrawn from operation awaiting an overhaul.