By the end of that year No. 5 Group completed its acquisition of No. 3 Group stations north of the Wash and, under its control, Finningley squadrons started conversion to the Handley Page Hampden, with Avro Ansons to fill out strength until more of this new type were available from production. The need to establish units devoted to training crews on the new bomber types resulted in the setting up of so-called pool squadrons during the summer of 1939. A revision of this arrangement brought the designated pool squadrons into operational training units and, shortly after war was declared, both the Finningley squadrons moved to RAF Upper Heyford to form one of these organisations. Finningley was to continue in a training role for No. 106 Squadron, which brought its Hampdens from RAF Cottesmore in October. Also classed as a reserve squadron, No. 106 continued the operational training role for No. 5 Group that the previous occupants had started to provide. During early 1940, Fairey Battles of 98 Squadron were moved to RAF Finningley from RAF Scampton. By August 1940 the critical war situation caused No. 106 to be placed on operational call. Most of its early sorties were to drop mines in the approaches to French Channel ports thought to be harbouring invasion barges. There was still need for a final polish for new Hampden crews and in February 1941 No. 106 left its 'C' Flight at Finningley to continue with this task while the rest of the squadron moved to RAF Coningsby for full offensive operations. While flying from Finningley, six Hampdens had failed to return. In March the former No. 106 "C" Flight metamorphosised into No. 25 OTU, initially continuing to train with Hampdens and Ansons. A few Manchesters arrived in the spring of 1941, and the unit was later bolstered with Wellingtons. Early in 1942 Finningley passed to No. 1 Group and with no further need for Hampdens or Manchesters No. 25 OTU concentrated on Wellingtons, nine of which were lost when the station was called upon to take part in Bomber Command operations. No. 25 OTU was disbanded in February 1943 and in March No. 18 OTU moved in from RAF Bramcote and began using RAF Bircotes and RAF Worksop as satellites. In November the Wellingtons were moved to these satellites as hard runways were to be laid at Finningley. These were put down during the