The first of the British aircraft took off at around 17:20 hours CET for the journey. This was a group of Lancasters from Bomber Command's 83 Squadron, No. 5 Group, acting as the Pathfinders, or flare force, whose job it was to find Dresden and drop magnesium parachute flares, known to the Germans as "Christmas trees", to light up the area for the bombers. The next set of aircraft to leave England were twin-engined Mosquito marker planes, which would identify target areas and drop target indicators (TIs)" that created a red glow for the bombers to aim at. The attack was to centre on the Ostragehege sports stadium, next to the city's medieval "Altstadt" (old town), with its congested and highly combustible timbered buildings.