squadron in raids against Essen and Hamburg. He had completed more than fifty operational sorties by the age of 23. With the Pathfinder Force In June 1942 ideas for helping bombers find their target more easily came to fruition with the creation of the Pathfinder Force. Each Group contributed a squadron to the new force. Marks and his 35 Squadron were selected from 4 Group. Marks had led his squadron on a remarkable 100 sorties without a crew loss. His was one of the five squadrons selected to form the Pathfinder Force. The squadron, with hand-picked crews from the group, along with their ground support staff arrived in RAF Graveley the first day the force was formed. Marks led his squadron on the first Pathfinder raid against Flensberg. Though a four engine heavy bomber with a 5,800 lb payload, the Halifax had a number of problems. Marks noted that the front gun turret partially obstructed the view of the pilot. He had it removed from his aircraft and replaced with a section of clear Perspex. The modification was reviewed by Handley-Page at the production center in Radlett and accepted. This change was incorporated into the production of Halifaxes in October 1942. Pilot visibility, however, was not the major problem with the Halifax. Leonard Cheshire, a friend of Marks who flew with him in Nos. 77 and 35 Squadrons, was experiencing problems with the aircraft as well. "The Halifax was temperamental. You learned to treat her with caution, but she wasn't really, we learned later, a safe aircraft. There was no margin of error when you got near to the stall. We suddenly became aware that nobody came back on three engines. I took the aircraft up and deliberately stalled her, and I found that you could not get out of the stall. The only way to get out of stall was to apply both opposite engines and both feet on one side of the rudder and use all your strength, and only then you just got out. So a man who had lost an engine while on ops had no chance." The Halifax was a significant concern for Bomber Command commander in chief Arthur Harris. In a letter to the Air Ministry in 1942, he wrote "The Stirling and the Halifax are now our major worries. They presage disaster unless solutions are found. Regarding the Halifax, nothing ponderable is being