They are throwback to the dawn of diesel on Britain's railways.
But in recent years, a fleet of four Class 37 engines have been pressed back into service on Norfolk lines, to meet a shortage of more modern locomotives.
The return of these 1960s workhorses has caused such a stir among rail enthusiasts that a special excursion trip on them is now being planned. A train, formed of four MkII carriages top-and-tailed by two Class 37 diesel locomotives, will run fans from Norwich to Ely and from Norwich to London, raising funds for East Anglia's Children's Hospices (EACH).
The Class 37s have been in regular use for the past 18 months on the Norwich to Great Yarmouth and Lowestoft lines.
And although they have been in operation for 50 years, it is more than 30 years since they were regularly in use on passenger services on the Norwich to Ely and Norwich to London routes.
The special service will run on Saturday, April 30, chugging from Norwich to Ely and back then from Norwich up the Great Eastern Main Line to London Liverpool Street and back.
It is hoped that this chance to travel behind these popular diesels on their former stomping ground will prove attractive.
Jonathan Denby, of Abellio Greater Anglia, said: 'We're delighted to be running this special Class 37 rail tour to raise funds for East Anglia's Children's Hospices. It's an extremely worthwhile cause focused on the region we serve and supported by many of our employees.
'Taking in two routes which have been synonymous with Class 37 locomotives in the past, we hope it will be very popular and generate an impressive contribution to EACH funds.
'It promises to be a great day out for all involved.'
The train operator is also auctioning two opportunities for a cab ride – one from Norwich to Ely and the other from Ely to Norwich.
Anyone booking on the tour can bid for this very rare opportunity to experience a driver's eye view of a rail journey.
Mark Loades, of EACH, said: 'We're thrilled this special one-off charter train will benefit our charity. It's a wonderful opportunity for rail enthusiasts to travel behind such popular locomotives, while also supporting local families.
'We're very grateful to Abellio Greater Anglia for their generosity and support, and would urge people to book their place quickly to avoid disappointment.'
Tickets cost £60 each, with 200 places on the service and all profits to EACH. Bookings can only be made online via www.greenrailtravel.co.uk/special.
Are you raising money for charity? Email reporter Sam Russell at sam.russell@archant.co.uk or call 01603 772568.
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