withdrawn. In 1935 the Milehouse to Devonport line closed following the delivery of the city's first diesel-engined buses. More were needed in 1936 to allow the closure of the line to Prince Rock and in 1937 to allow the withdrawal of the two long circular routes. It was at this time that the bus routes were first numbered. The plan to close the remaining tram lines was put on hold because of the outbreak of World War II in 1939; they were powered by electricity generated by British coal, whereas the buses relied on imported fuel. The one remaining route, from Theatre to Peverell, kept running but following city centre bomb damage in April 1941 (when car 133 was destroyed) the service was only operated between Drake's Circus to Peverell until the final tram ran in September 1945. A large part of the population of Plymouth moved out to the relative safety of the countryside during the war which meant that the Corporation's buses and trams were carrying fewer passengers, but rival Western National was under increasing pressure. Both operators had suffered damage to their depots and fleet – Milehouse was bombed in April 1941 – and so the two companies decided to pool resources under a Plymouth Joint Services agreement. This took effect from 1 October 1942 and resulted in 80% of mileage in and around the city were to be operated by the Corporation and 20% by Western National; the receipts were also divided in the same proportion, irrespective of which company operated which routes. This allowed Plymouth buses to operate beyond the city boundary to places such as Yelverton, Plympton and Wembury, while Western National were now allowed to pick up local passengers within the city where they had previously been restricted to only those travelling beyond the boundary. The Plymouth Joint Services agreement remained in place after the war, enabling both the Corporation and Western National to serve new housing estates that sprang up around the edge of the city. The routes in the Joint Services area, including those of Western National, were renumbered in a single sequence from 1 to 57 in 1957. Buses with front entrances were delivered to Plymouth City Transport from 1960 which paved the way to conversion of routes to one man operation from 1968, the first operator in the South West of England to do so. To help speed boarding