Due to its sheer level of use, and toughness due to its heavy armor and radial engine, the P-47 was arguably the most effective. The P-38, and to a lesser extent, the P-51, were also used as ground attack aircraft, but were more vulnerable due to their liquid-cooled engines; P-47s could have whole cylinders shot off, while a single bullet through a coolant line would doom a P-38 or P-51. The majority of Ninth Air Force fighter groups operated the P-47, while only a handful of others used the P-38 or P-51;
| Group | Aircraft |
|---|---|
| 36th | P-47 |
| 48th | P-47 |
| 50th | P-47 |
| 354th | P-51 |
| 358th | P-47 |
| 362nd | P-47 |
| 363rd TRG | P-51 |
| 365th | P-47 |
| 366th | P-47 |
| 367th | P-38 (to P-47 February 1945) |
| 368th | P-47 |
| 370th | P-38 (to P-51 February 1945) |
| 371st | P-47 |
| 373rd | P-47 |
| 404th | P-47 |
| 405th | P-47 |
| 406th | P-47 |
| 474th | P-38 |
Keep in mind that the overall effectiveness of aircraft against tanks is usually greatly overstated. The .50 caliber machine guns carried by the P-38, P-47, and P-51 were generally ineffective against the roofs of German tanks. The angle of attack and speed of the aircraft mostly negated the penetration ability of the .50 BMG round, although ventilation grilles were vulnerable; the claims of pilots who bounced rounds off of the ground and into the lower front belly plates of German tanks can probably be discounted. Most rockets were hideously inaccurate; the British performed a test where a Panther tank was painted stark white with large black crosses and placed in the middle of an open field. 64 RP-3 rockets were fired at the Panther from four Typhoons making careful passes at it, yielding only three direct hits (4.63 percent accuracy) The British estimated that it took 800 rockets or 3,500 bombs to score a direct hit on a tank during battle conditions;
Near La Baleine, France, Typhoons conducted 99 sorties on a German armored column consisting of ~50 tanks. The pilots claimed to have KO’d 17 of the tanks. The British Army’s No. 2 ORS investigated the area and found that there was [only] a total of 9 tanks, 2 of which were actually destroyed by rockets, or just 11% of the original claim. Around Mortain, the U.S. and British pilots claimed to have destroyed or probably destroyed a total of 120 tanks. The actual number of destroyed AFVs in the area was close to 45 tanks. Only 9 seemed to be victims of airstrikes, or 7% of the original claim. At the Falaise Gap the Fighter-Bombers claimed 3 times more tanks (391) than the Germans actually lost (133). The number of tanks lost to aircraft seemed to be 15 in the Falaise area, or 4% of the original claim
On the U.S. side, the use of M10 three-tube rocket launchers was abandoned by the 56th Fighter Group in August 1944 after two missions due to their poor accuracy and excessive drag. 5-inch HVAR rockets fielded beginning in late 1944 were no better; the force of ejected shell casings and ammunition belt links often broke the firing wires or dinged and bent the sheet metal fins of the rockets, and many pilots griped that they couldn't hit anything to begin with. Near-misses with 500-pound bombs (262 pounds of explosives) were capable of flipping tanks or stunning their crews enough to force them to run away and abandon the vehicles, but their accuracy was also poor, even worse than that of rockets as demonstrated above.
Sources:
Air Power at the Battlefront: Allied Close Air Support in Europe 1943-45, by Dr. Ian Gooderson
Air Power in the Age of Total War, by John Buckley
Air Power: The Men, Machines, and Ideas that Revolutionized War, from Kitty Hawk to Iraq, by Stephen Budiansky
C. Lawrence & N. Zetterling @ The Dupuy Institute Forum
operationbarbarossa.net (dead link)
Zemke's Wolfpack: A Photographic Odyssey of the 56th Fighter Group During the Second World War, by Nigel Julian and Peter Randall
Angels Zero: P-47 Close Air Support in Europe, by Robert V. Brulle