|Engine:||2 Bristol Siddeley Maybach MD650 diesels|
|Power:||2, 200 hp (1, 641 kW)|
The Class 42 was powered by two Maybach diesels built under licence by Bristol Siddeley. The first few locomotives were limited to 2,000hp due to limitations with the transmission though most of the class was rated at 2,200hp. One locomotive was fitted with a pair of Paxman 12YJXL diesels and was rated at 2,400hp. The Class 42 looked very similar to the V200 class though originally British Railways wanted it to look different, their designs were later used on the Class 52 .
The locomotives had a successful entry into service, Western Region found they could comfortably handle heavier trains than the Class 40. However there were problems with riding at high speeds which resulted in speed restrictions until bogie modifications could be carried out in 1960 . Most of the class were named after Royal Navy ships and hence the nickname of the class became "Warships".
As with the other diesel-hydraulic designs the Class 42 was doomed once British Rail, in it's drive for standardisation and rationalisation, had sufficient diesel-electric motive power to take over their duties. Withdrawals began in 1968 and were completed by 1972 . Two Class 42s have been preserved.
|D832 Onslaught at Wirksworth|
|818 in BR blue (KD Collection)|
|D832 at Duffield|
|D832 brings a train into Wirksworth|
 John Jennison & Tony Sheffield, Diesel Hydraulics of the 1960s and 1970s (Ian Allan, 2014) p. 4
 David Lawrence, British Rail Designed 1948-97 (Ian Allan, 2016) p. 107
 Brian Haresnape, Western Region Diesel-Hydraulics (Ian Allan, 1982) p. 28
 Pip Dunn, British Rail Main Line Locomotive Specification Guide (Crowood Press, 2013) p. 80