British Rail Class 55 Deltic

The Deltic concept emerged from the Napier-built Deltic engine — an 18-cylinder triangular opposed-piston diesel originally developed for naval fast patrol craft. English Electric proposed using a pair of these engines, each 1,650 hp, in a single Co-Co diesel-electric locomotive — an ambitious 3,300 hp double-engined design that would offer Pacific-class power without coal handling. The prototype "Deltic" of 1955 (later DP1) demonstrated the concept; 22 production engines were built 1961–62 for the East Coast Main Line.

The Class 55 hauled the principal East Coast expresses — King's Cross to Leeds, Newcastle, Edinburgh — from 1962 until 1981, when displaced by the Class 43 HSTs. Six preserved across the railways; some run regularly, others on static display. Highly distinctive, much-loved, and for many enthusiasts the high-water mark of British dieselisation.

Co-Co diesel-electric, 3,300 hp, twin Napier Deltic D18-25 engines. Distinctive sloping nose ends with single forward-facing lamp.

• D9000 Royal Scots Grey, D9002 Kings Own Yorkshire Light Infantry, D9009 Alycidon, D9015 Tulyar, D9016 Gordon Highlander, D9019 Royal Highland Fusilier (all preserved)