Martin Gilbert 
D-Day [PDF ebook] 

"The Allied landings in 1944 had all the prospects for disaster. Churchill thought he would be woken up to be told of massive casualties. Eisenhower prepared a somber broadcast announcing that the enterprise had failed.The specter of failure was always present. After a failed landing the Nazi regime would have regained the ascendant. New, terrifying bombs and rockets were ready to be launched. Long-distance submarines were in the final stage of development. The last million Jews of Europe were listed for deportation and death.Failure at Normandy could have given Hitler the chance of continuing to rule western Europe, particularly if the United States, bloodied and defeated in Normandy, had decided-after two and a half years of focusing on Europe-to turn all its energies to the ever-growing demands of the Pacific, leaving Europe to its own devices. Had that happened, I doubt if I would have been alive to write this book, or free to express my opinions without fear of arrest."–Martin Gilbert