Construction of the Central line's eastern extension was started in the 1930s, and the tunnels were largely complete at the outbreak of the Second World War although rails were not laid. The facilities at Bethnal Green were requisitioned in 1940 at the onset of the first Blitz and administration was assigned to the local authority, the Metropolitan Borough of Bethnal Green, under the supervision of the "Regional Commissioners", the generic name for London civil defence. Heavy air raids began in October and thousands of people took shelter there, often remaining overnight. However, usage of the shelter dwindled in 1941 as the air forces of Germany and Italy were redirected away from the United Kingdom and against the Soviet Union. A relative lull occurred although the number of shelterers rose again when retaliatory bombing in response to Royal Air Force raids was expected.