OSS Commando: Final Option by Charles Sasser
A military thriller set in the final days before the D-Day invasion in 1944. The hero is Captain James Cantrell, a former Chicago homicide detective, now a member of the OSS (Office of Strategic Services). His mission is to keep the secret of the D-Day landing location from the Germans. He has a landing craft sunk underneath him, survives a bombing attack in downtown London, parachutes into Nazi occupied France, breaks into a heavily guarded castle, and has not one, but two beautiful women to deal with. One a Nazi spy and other a member of the French resistance forces.