Build and Introduction

The High Speed Diesel Train (HSDT) was authorised by BR in the early 1970s as a stopgap during development of the Advanced Passenger Train (APT). Following evaluation of the prototype set and a change of name to the High Speed Train (HST) BR put together a proposed plan for HST introduction. Sets were ordered in batches starting with 27 for the Western Region, followed by 32 for East Coast Main Line (ECML) duties. Further orders followed with 14 sets ordered for West of England services and 18 sets for Cross Country use. A final order was for four additional 8 coach sets for use on the ECML, though these were in fact delivered before the Cross Country sets. Following the difficulties in obtaining investment approval for this final batch, BR concluded that the likelihood of further successful investment submissions was low and the HST production line shut after 95 sets had been delivered.

The first production HSTs entered service on British Rail's Western Region in August 1976, with 125mph running implemented from that October's timetable change. The 7 coach sets were used on services between Paddington and Bristol/South Wales and allowed the 125mph capability of the sets to be fully utilised over much of these routes. Maintenance allocations were divided between Bristol St. Philip's Marsh and Old Oak Common, purpose built facilities were provided at both depots.

HSTs made their debut on the ECML in 1978 and there followed a programme of line-speed improvements that enabled them to operate to their full potential. Initially services ran from Kings Cross to West Yorkshire, Newcastle, Edinburgh and Aberdeen, all using 8 coach sets. As business grew, HSTs started reaching new destinations such as Hull, Cleethorpes and Middlesbrough. To cater for this an extra four 8 coach sets were ordered, although five sets were actually delivered with one set diverted from the second tranche for the Western Region. Four new or refurbished depots were provided at Bounds Green, Leeds Neville Hill, Newcastle Heaton and Edinburgh Craigentinny. Heaton was used at first as the commissioning depot, though this role was later undertaken by Neville Hill.

The earliest years of HST operation coincided with a change from the traditionally engineering led railway to one that was more commercially driven. From their introduction HSTs had proved popular with the travelling public resulting in a significant increase in passengers and, of course, revenue. This became known as the 'nose cone effect' and is perhaps the only equivalent in diesel traction of the well known 'sparks effect' that invariably accompanies electrification schemes. As their commercial appeal became recognised, HSTs were no longer restricted to those routes that did justice to their high speed capability. They were introduced to new routes not noted for high speed running but where there was considerable passenger demand for them.

West of England services were always considered for HST usage, even though full 125mph running is limited to the stretch from Paddington to Reading. However, HSTs offered an attractive commercial proposition and thirteen seven coach sets were built, fully entering service in May 1980 from Old Oak Common and St. Philip's Marsh depots, following a series of problems as a result of a change in traction motor supplier.  Plymouth Laira depot was upgraded to carry out servicing and to accommodate the allocation of new HSTs for the next and final batch of HSTs on the North East - South West route. Whilst there was limited scope for high speed running along the Cross Country lines, their superior acceleration and braking still made it possible to reduce journey times. Coupled with the 'nose cone effect' already mentioned, HST was felt to be a worthwhile investment and eighteen 7 coach sets were built, entering service from late 1981.