What is the theme in Pegasus Bridge: June 6, 1944 by Stephen E. Ambrose?

Training is another dominant theme of the book. The men involved in the bridge operation began their training two years before the invasion, not knowing what they were training for. The British airborne forces were formed in 1942, when Jim Wallwork volunteered. He trained on small planes and on gliders. They trained to fly and land in the dark using a stop watch to navigate by. They would not have any use of landing lights or be able to discern any landmarks in France until they were just about to land.