British Railways' (BR) Type 4 "Warship" class diesel-hydraulic locomotives were introduced in 1958. It was apparent at that time that the largest centre of expertise on diesel-hydraulic locomotives was in Germany. The Western Region of British Railways (in view of post-World War II sensibilities) negotiated a licence with German manufacturers to scale down the German Federal Railway's "V200" design to suit the smaller loading gauge of the British network, and to allow British manufacturers to construct the new design. The resultant design bears a close resemblance both cosmetically and in the engineering employed. They were divided into two batches: examples built at BR's Swindon works were numbered in the series D800 to D832 and from D866 to D870, had a maximum tractive effort of 52,400 pounds force and are the British Rail Class 42 of this article. 33 others, D833-865, were constructed by the North British Locomotive Company and became British Rail Class 43. They were allocated to Bristol Bath Road, Plymouth Laira, Newton Abbot and Old Oak Common.