Hydraulic Pioneers - The NBL "Warships"

The 1955 modernisation programme for British Railways called for the end of steam locomotive production by the end of the decade and that electrification and re-signaling schemes should be implemented as quickly as time allowed. The future plan involved a 15 year period, and where electrification was neither possible or viable the introduction of diesel locomotives should begin. The BTC authorised the production of a number of locomotives with a view to access their qualities and to obtain experience in operating them. They were to be trailed for a three period and information gathered over this time was then to be used for production orders of a full fleet of diesel traction. The pilot orders consisted of 174 machines, 160 of which had electric traction, the remaining 14, hydraulic. The Western Region adopted the latter in an inaccurate belief that the fluid drives would be far more easier to both repair and maintain, but in hindsight were far more complex than their electrical counterparts. The first 'C' type or Type 4 prototype locomotives delivered to the Western Region were the five NBL 'Warships', D600 - D604. (Contrary to popular belief, the locomotives were never designated Class 41.) Built by the North British Locomotive Company, the units featured two 1,000hp NBL/MAN L12V18/21BS engines coupled to Voith transmissions powering two A1A - A1A bogies. Each unit weighed in at 117tons 8cwt in working order, were 65ft long over buffers, a 90mph maximum speed, and had a tractive effort of 50,000lbs. D600 entered service with its Warship 'Active' name in January 1958 based at Swindon, followed by the next four, progressively, over the following year.



NBL Works No.

Date Introduced

First Allocation

Date Withdrawn

Final Allocation





82C (Swindon)




Ark Royal



82C (Swindon)







83D (Laira)*







83D (Laira)*







83D (Laira)*



*1948 allocated depot code. Laira changed to 84A in September 1963.
**D600 Active became the first diesel locomotive to be named.

The main equipment in each locomotive was centred symetrically around a Spanner train heating boiler and consisted of (from the centre of the locomotive to each cab) the dynastarter, engine and transmission block. The cooling fans and radiator blocks were situated above and beside the transmission blocks respectively, and were located in compartments of their own. Engine exhaust left the roof at the transmission end of the engine. Each locomotive carried two fuel tanks, located above the dynastarters and were unusually of differing sizes, one holding 475 gallons and the other, 375 gallons. The body itself consisted of thick riveted and welded 'I' sections for the underframes complete with large gauge steel floorplates and cast steel dragboxes. To offset this enormous weight, the resulting bodysides, cabs and inner compartments were produced in alluminium. In 1960, D603 Conquest  was involved in a serious collision which resulted in the need for the replacement of both cabs. It is reported that the new cabs were produced in sheet steel, as the original light alloy producer was no longer interested in manufacturing odd small cast and fabricated parts. A further modification on all locomotives saw the upper bodyside radiator louvres changed, possibly to accommodate air filters.

Production of D600 at the NBL Glasgow workshops. Of note is the thick steel underframe which, when combined with the two A1A - A1A bogies required an aluminium body to offset weight.
(Photo North British Locomotive Company)

Cab detail of D600 after completion by NBL.
(Photo North British Locomotive Company)

Each of the MAN L12V18/21A engines were set to 1000bhp at 1445rpm, and on D600/ 1 were supplied from the manufacturers works in Augsberg, Germany. Those for D602 - 4 were built, under licence, by NBL themselves and in an effort to cut down on future European dependence, all ancillary equipment was changed to that of British manufacture or supply; D600/ 1 engines were suitably converted at later dates. No future interchangeability of either engines or transmissions was envisaged, and thus various connections, pipes etc were made as and where needed. Mulitple working was only possible with other members of the class and the first six (D6300 - D6305) Class 22 locomotives; an orange square code denoting this was applied to the bufferbeams.
Livery when introduced was all over Brunswick Green with a 4in wide light grey waist stripe the length of the body inbetween the cabs. Bufferbeams were picked out in red whilst all underslung equipment and bogies were black. The alluminium nameplates had polished letters on a red background plate. Standard 6in numbers were applied under each cab side window, and beneath these were the brass diamond worksplate of NBL's Queen's Park factory. Only one locomotive, D600 carried the full rail blue livery but a second, D602, ran in blue but with small yellow warning panels applied to the fronts. All five locomotives were built as new with disc type route indicators fitted to the front ends and later on in their lives received split alpha-numeric headcode boxes.

One of the five Warships leaving NBL's Queens Park Factory after completion, with numbers, nameplates and front end headcode discs still to be fitted. All the locomotives were trailed in Scotland before movement to the WR.
(Photo North British Locomotive Company)

The official completion date for D600 was November 25th 1957, but after this the locomotive began a short period of trials in Scotland with trains of varying loads, before movement to the Western Region and introduction in January 1958. D601 followed in the following March, but it was to be in November of the same year that the rest of the class were steadily introduced. On the 17th February 1958, a press demonstration run was organised from Paddington to Bristol and return involving the use of D600, a run that would inadvertently prove the versatility of the twin engined locomotives. On the return journey, soon after leaving Bristol, one of the MAN engines unexpectedly cut out, leaving the locomotive to continue its last 100 miles on one engine, and no doubt giving glowing reports in the media the following day as to the advantages of the new diesel traction!
Various trials with the class continued over the next few months and on June 16th 1958 became the first diesel locomotive to haul the 'Cornish Riviera Express'. D601 Ark Royal   was coupled to a 10 coach, 375 ton (the maximum for the class) load for the run from Paddington to Plymouth and completed the non stop journey of 225 miles in 240 minutes with a fuel consumption of between 220 - 240 gallons. Thus, a complete round trip to Devon from the capital could be made on both tanks of fuel, even with the train heating boiler in operation.

D602 Bulldog at Newton Abbot in 1961 seen paired with an unidentified 'Castle'.
The steam locomotive was possibly required for assistance over the Devon Banks.
(Photo courtesy David Happs)

On what have must been one of its first passenger duties, D602 Bulldog enters Sonning Cutting with a Paddington bound
train in 1959.
(Photo courtesy The David Hills Collection)

D600 Active approaches Dawlish with the up Cornish Riviera Express in September 1961.
(Photo David Happs)

The class continued to operate the fastest Bristol and West of England trains until the introduction of the D800 'Warships', when the latter seemed to find favour with Western Region staff, possibly due to to the easier servicing and maintenance procedures of the British Railways designed and built machines. The D600's became relegated to block oil trains and fully fitted freights. Further reduction in their duties in later years, saw the class employed on china clay traffic in Cornwall and it was at this time they rarely ventured north of Exeter. A final move came in the twilight months of their lives when they were transferred to Landore to work mineral services vacated by Class 37's transferred to the Eastern Region.
The class were always synonymous with Laira depot, and it was to here they returned in December 1967, now deemed withdrawn and destined for the scrapman after a short life of just nine years.
The pioneer Warships became the first victims of a BRB policy approved in 1967 to reduce by 1974 the number of main line diesel locomotives from 2976 in 28 classes, to 2240 in 15 classes, priority being types that had given trouble, had high maintenance costs or, to be of too few numbers to be regarded as 'standard'. Clearly, the D600's fell into all three catagories, and the three criteria became the downfall of all the diesel-hydraulics by 1977.
In July 1968 the five locomotives left Laira for the last time, D600/ 1 were hauled by  Class 35 Hymek locomotive No. D7055 on the 22nd, to Woodhams at Barry, finally arriving at their destination on the 28th of the month; D601 went on to become the subject of a further 'claim to fame', detailed further on this website here. D602 - 4 moved to South Wales also, on the 29th of the month, this time behind Class 52 Western No. D1006 Western Stalwart , but to Cashmores yard at Newport; D604 was reduced to scrap in September of the same year followed by D602/ 3 in the November.

End of the line for D604 Cossack at Cashmores in August 1968. One cab
has already been removed, whilst the bulk of the locomotive remains to
be reduced to scrap in the foreground.
(Photographer unknown)

D602 Bulldog pictured at Plymouth supporting its early rail blue livery with small yellow warning panels. The locomotive also displays the later addition of the four character headcode 'split' boxes located  either side of the nose end connecting doors, which clearly spoil the original front end appearance of these machines. D602  ended its days at Cashmores, Newport in November 1968.
(Photographer Alec Swain)

The 21st century sees these rare nameplates commanding very high prices on the enthusiasts market. D604's pictured here, could well be worth in excess of 10,000. The plate is seen here with its new owner!
(Photographer unknown)


Technical Specifications:

Class: BR Type C, Class D20/2, later 20/4..
Purpose: Heavy duty locomotives.
Introduced: 1958.
Numbers: D600 - D604.
Engines: Two NBL/ MAN 12-cyl. 4-stroke L12V18/21BS of 1000hp. 7.1in bore, 8.3in stroke. Maximum continuous rated output, 1000hp at 1445rpm.
Transmission: Hydraulic. Two Hardy Spicer cardan shafts to Voith-North British type L306r hydraulic transmissions, each containing three torque converters.
Weight: 117tons 8cwt.
Performance: Maximum tractive effort: 49460lbs at 27.6% adhesion.
Braking: Air for loco and vacuum for train giving a brake force of 75.13% of loco weight in working order.
Maximum Speed: 90mph (maximum permitted working).
Train Heating: Steam. Spanner Swirlyflo boiler with 2000lb/hr steaming capacity.  
Curve: Minimum curve negotiable, 4.5 chains.
Tank Capacities: Engine fuel & train heating fuel, 800gal. Steam heating boiler 1000gal.

Notes: Worksplate from D603 sold at auction 10.07 for 3,100.

Further Interest On This Site:-

The Class 35 'Hymeks'
The Class 42 'Warships'
The Class 52 'Westerns'



D600 Active & D601 Ark Royal at Woodhams Scrapyard

Timeline 1958 -1982