In the United States, where the railways are 90 per cent. dieselised today, diesel-electric power is the unvarying rule for independent locomotive units, and the only motive power exceptions are the highly successful 600-h.p. diesel-hydraulic railcars of the Budd "RDC" type, of which between 300 and 400 are now at work.
Source: wiktionary
In November 1959, a paper entitled "The Swindon-built Diesel-Hydraulic Locomotive" was presented to the Institute of Locomotive Engineers by Mr. G. E. Scholes and it contained some very interesting figures. One set was a comparison between the mileages achieved during a period of the first five months in 1959 by "King" and "Castle" 4-6-0s and "Britannia" 4-6-2s and those of D800 to D805, the first of the Swindon-built 2,000 h.p. diesel-hydraulic locomotives of the "Warship" class, then brand new and subject to the teething troubles of all such complicated units in the earliest stages of their use.
Source: wiktionary
The elimination of vacuum-braked wagons would be slowed down, and the Western Region's flirtation with diesel-hydraulic locomotives was questioned.
Source: wiktionary