'Mons Meg' is a stunning example of one of Nigel Gresley's P2 engines, sporting a stylish green livery. It has sprung metal buffers and NEM tension lock couplings, with a 21-pin socket ready for upgrade to HM7000 control. Nigel Gresley designed the P2s for hauling heavy express trains along the demanding route between Edinburgh and Aberdeen. Six were introduced between 1934 and 1936. The first three locomotives differed in appearance, the third having the wedge-shaped front similar to the A4s which was adopted for the remainder of the class. The first two also later converted. Even then, 2004 was fitted with an experimental butterfly valve blastpipe bypass and the last two also had design differences, meaning that none of the six were built the same. All were subsequently rebuilt by Thompson as conventional Pacifics in 1943/4 by Gresley’s successor, Edward Thompson.