The Sins of the Father (The Clifton Chronicles-2) by Jeffrey Archer

It is only days before Britain declares war on Germany. Harry Clifton, hoping to escape the consequences of a family scandal, and realizing he can never marry Emma Barrington, has joined the Merchant Navy. When a German U-boat sinks his ship, Harry and a handful of sailors are rescued by the SS Kansas Star, among them an American named Tom Bradshaw. That night, when Bradshaw dies, Harry seizes a chance to bury his past?by assuming the man`s identity.