The main raid on Darmstadt was by No. 5 Group RAF on the night of the 11/12 September 1944, when 226 Lancasters and 14 Mosquitos were directed to the medieval city centre, as houses there were mainly built of wood. The raid was to incorporate a new technique where, instead of bombers flying along a single path across the target, the bombers would bomb along a fan of paths over the city. The intention was to deliberately spread the bombload. The attack started a fierce fire in the centre and in the districts immediately to the south and east. The destruction of dwellings in this area was almost complete. The RAF lost 12 Lancasters, 5.3 per cent of the bomber force, having encountered an unusually large number of German fighters.