 On the night of 18 June, a dress rehearsal was held, with the Pathfinders illuminating and marking a target on the bombing range at RAF Wainfleet, on the Lincolnshire coast, for the 5 Group force.The crews were confined to camp when not flying and were forbidden to use the telephone.Group Captain Slee held the full briefing for the 25 Pathfinder and 5 Group crews based at Scampton on the morning of 19 June.