In the climactic scene of the highly-acclaimed Saving Private Ryan, the beleaguered Ranger and Airborne forces of Captain John Miller (Tom Hanks) are about to be overrun. Against overwhelming odds they have fought to save a crucial stone bridge over the Merderet River. It is a losing battle. With defeat imminent, the Americans retreats across the bridge and prepare to blow it. However, before that can happen, Captain Miller is shot and is unable to detonate the explosives. As a German tank rumbles across the bridge it appears all is lost. Then, in typical Hollywood tradition, the calvary arrives--two P-51 Mustangs. With uncanny timeliness and pinpoint accuracy they knock out the German tank on their first pass without destroying either the bridge or the American infantry who are mere yards away.
Though this may be a fitting end to a very good movie, it is not representative of the capabilities of tactical air power, especially early in the Normandy campaign. Leaving aside the question of accuracy, the system of air support in place at the outset of the invasion was much too cumbersome to allow an intervention of this nature. The Americans went into Normandy with a system of Close Air Support (CAS) that was largely derived from the British experience in North Africa. It was based on the belief that centralized contrl of air assets was the most effective method of employment. However, following D-Day, the system in place was far too unwieldy to provide effective support. Over the next three months, most of the existing doctrine was effectively discarded. An air support organization emerged that was the complete antithesis to that with which the Americans had started. The system which evolved proved to be highly effective, flexible and able to adapt quickly to a variety of situations.
Bechthold, Michael "“The Development of an Unbeatable Combination”: US Close Air Support in Normandy." Canadian Military History 8, 1 (1999)