I have watched saving Private Ryan several times. Every time I hear the characters at the end say "P-51 TANK Busters" it makes me laugh.

THERE WAS NO SUCH THING.

The P-51C and P-51D was intended as an air superiority fighter for use against enemy aircraft. They used the same Rolls Royce engine (RR-Merlin) as the Spitfire MkIX but built under contract by Packard (Packard-Merlin). The P-51D was built for speed at altitude against advanced German fighters.

Many P-51 flew on D-Day- mostly at altitude to keep the Luftwaffe from being able to launch ground attack missions over the beach head. This was successful as only two German fighters (BF-109s) flew over the Normandy beaches on D-Day.

(The early underpowered non-supercharged P-51s "Mustangs bought by the RAF were used for ground attack in 1940 and 1941. The USAAF briefly used the Allison Powered P-51A/B in this role.)

Also the USAAF generally did not employ single engine attack aircraft in close air support of ground forces. German ground units were equipped with too many 20mm, 37mm and 88mm cannon to make this a feasable tactic.

The Army Air Corps generally used the P-47 for ground attack role against convoys and trains with 5 inch rockets well behind German lines. The P-47 was a very much LARGER more robust plane (a P-51 looked like a toy beside one) with a very tough air cooled Pratt and Wittney WASP radial engine. The P-47 also carried eight .50 caliber machineguns (vs. P-51s six) and when these were equipped with armor piercing bullets these were very effective against convoys -including tanks moving to the front- and locomotives. Each P-47 could also carry about twice the bombs or rockets of a P-51. The P-47 could carry a 1000lb bomb AND eight rockets on the same mission (the P-51 could carry two 250s OR six rockets but not both at the same time.) The P-47 was generally not used for close air support of us forces. The US Army doctrine of the time greatly favoring massed artillery fire or medium bombers instead.

THE USMC did develop and perfect close air support in the Pacific Theater of Operations but that's another story.

Late model P-51s such as the P-51Ds in the movie were generally restricted to altitudes above 5000 ft over enemy territory. They were generally used for escort and air superiority missions (fighter sweeps etc).

I believe most of the ground attack squadrons used over the Normandy beach area were actually RAF Typhoons or Tempests. Some of these may have executed missions over the American beaches- I don't know. i do believe there were scheduled breaks in the naval shelling on d-day when allied aircraft reconnoitered and bombed over the lodgment area.) The P-47 was generally used for "deeper" attacks against German ground units in rear areas.

It is my understanding that the USAAF mostly used medium bombers over Normandy. These flew parallel to the coast and bombed targets from medium altitudes so as not to conflict with naval gunnery or shore based artillery.