Francis Mackay 
Overture to Overlord [PDF ebook] 
The Preparations of D-Day

The book describes the problems of instigating resistance in France and the slow development of the clandestine warfare and special operation forces, equipment, training, delivery, communication, command, control and intelligence techniques.It covers the wide variety of organizations involved including OSS, SAS, US Operational Groups, Polish 'Bardsea’ teams, Jedburgh and Sussex teams, Inter-Allied Missions, MI9, Evasion and Escape Groups, Special duties/Carpet Bagger Air Delivery Squadron, The Secret Flotillas and Radio security and surveillance services.The book starts at close of Operation Dynamo and ends with Operation Titanic, the SAS deception ploys and the last of the pre-invasion activities.