It was introduced in 1945 as a two-cylinder rebuild (with diagram 100A boiler) of the three-cylinder LNER Class B17.

The LNER renumbered its locomotive stock during the period that these locomotives were being rebuilt, so some were renumbered at the time that they were rebuilt, some before rebuilding, and some after rebuilding.

The second renaming occurred after the withdrawal of 61671 in September 1958: in October, the name Royal Sovereign was transferred to no.

Two B2s were kept at Cambridge for hauling the Royal Train in East Anglia,[4][5] predominantly to and from Wolferton which was the nearest to Sandringham House, these being renamed Royal Sovereign and 61617 Ford Castle as the reserve.

[8] Due to the size of the turntables on the Great Eastern section, locomotives were sometimes used with tenders that were shorter than those originally designed.