of this sub-class. The vast majority were boilered and designated 251 AV. The four without train heating were designated 251 BV. In due course, when it was decided to fit dual braking to a number of locomotives, those previously 251 AV became 251 CX and one of the 251 BV (25032) became 251 DX. Class 25/2 Number sequence (original) D5233–D5299, D7500–D7597 (TOPS) 25 083–25 247 The Class 25/2 locomotives featured restyled bodywork and two-tone green livery similar to that carried by the Brush Type 4 (Class 47). The majority were built at BR Derby. The redesign principally affected two areas, the cab and the location of the air intakes. The gangway doors fitted to the earlier examples were rarely used, their presence adding to the complaints of noise and draughts in the cabs and the removal of these allowed the centre windscreen to be enlarged, so that its lower edge lined up with the windscreens on either side giving a noticeably different front end look. The removal of the air filters from the side air louvers to the cantrail was the result of a comparison carried out at Inverness between a batch of Derby built Type 2s and a batch of BRCW Type 2s (Class 26 and Class 27), the tests targeting the air quality within the engine room. These tests revealed the location of the grilles on the Derby build allowed for much more debris to reach the filters (especially the lower ones), clogging them quicker, leading to poorer air quality within the engine compartment, and so potentially affecting performance and engine wear. With such a large order to be completed it was felt that a redesign of these areas would have cost savings in the long run, in addition to a better working environment within the cabs, and with a general less cluttered look about the locomotive's exterior. Some class 25/2s were built at Darlington works, including D7597 (later 25247) which was the last locomotive to be built at Darlington. The 25/2s built at Darlington had the original bodywork, not the restyled design. There were six variants of this sub-class, reflecting that locos were boilered and/or vacuum braked and/or dual braked. Boiler fitted locomotives included the first five (252 AV) and final thirty Class 25/2 (252 DV). Only members of the latter batch were modified for dual brake operation becoming 252 CX with the exception of 25242 that