On a trip to Normandy in 1949 Cornelius Ryan became interested in telling a more complete story of Operation Overlord than had been produced to date. He began compiling information and conducting over 1000 interviews as he gathered stories from both the Allies and the Germans, as well as the French civilians. In 1956 he began to write down his World War II notes for The Longest Day: 6 June 1944 D-Day, which tells the story of the D-Day Invasion of Normandy, published three years later in 1959. It was an instant success, and Ryan helped in the writing of the screenplay for the 1962 film of the same name. Darryl F. Zanuck paid the author US$175,000 for the screen rights to the book. Cornelius Ryan’s 1957 book One Minute to Ditch! is about the successful ocean ditching of a Pan American Boeing 377 Stratocruiser. He had written an article about the ditching for Collier’s in their 21 December 1956, issue and then expanded it into the book. His next work was The Last Battle (1966), about the Battle of Berlin. The book contains detailed accounts from all perspectives: civilian, American, British, Russian and German. It deals with the fraught military and political situation in the spring of 1945, when the forces of the western allies and the Soviet Union contended for the chance to liberate Berlin and to carve up the remains of Germany. This work was followed by A Bridge Too Far (1974), which tells the story of Operation Market Garden, the ill-fated assault by allied airborne forces on the Netherlands culminating in the Battle of Arnhem. This work was also made into a major 1977 film of the same name.

Cornelius Ryan was awarded the French Legion of Honour, and an honorary Doctor of Literature degree from Ohio University, where the Cornelius Ryan Collection is housed (Alden Library). He was diagnosed with prostate cancer in 1970, and struggled to finish A Bridge Too Farduring his illness. He died in Manhattan, while on tour promoting the book, A Bridge Too Far, only two months after publication. Four years after his death, Ryan’s struggle with prostate cancer was detailed in A Private Battle, written by his wife, from notes he had secretly left behind for that purpose. He is buried in the Ridgebury Cemetery in northern Ridgefield, Connecticut, USA. For many years Ryan’s editor at Simon & Schuster was Peter Schwed who was assisted by Michael Korda. Ryan’s literary agent was Paul Gitlin.