The Soviet AF also produced and used huge numbers of the Ilyushin Il-2 ‘Sturmovik’ aircraft.
The USAAF and RAF on the other hand were guided by the doctrine of strategic bombing. For that reason they invested huge resources on heavy bombers but did not produce a specialized ground attack aircraft like the Germans and Soviets. Instead they used in that role their standard fighter aircraft Hurricane, Typhoon, P-40, P-47, P-51.
How did these planes perform in battle? Many history books claim that swarms of Allied fighter-bombers destroyed whole German armored units and paralyzed enemy movements. German generals attributed their defeats to crushing Allied air superiority.
The book ‘Air Power at the Battlefront: Allied Close Air Support in Europe 1943-45’ by Ian Gooderson tries to answer this question by analyzing the information collected by Operational Research Sections during the war.The ORS teams included both military and civilian personnel and their goal was to collect information regarding enemy losses and performance of weapons from the battlefield.
Their studies of battles in NW Europe from summer 1944 to the end of the war showed that fighter bomber units overstated their kills by a very wide margin and that heavy bomber attacks caused little damage to German troops due to their wide dispersion.
For example the German attack near Mortain was supposed to have been defeated mainly through air attacks. Allied pilots claimed over 200 tanks destroyed and the German general Hans Speidel wrote: ‘it was possible for the Allied air forces alone to wreck this Panzer operation with the help of a well coordinated ground to air communications system’. However when the area was examined by No2 ORS and ORS 2nd TAF only 46 tanks and self-propelled guns were found and of these only 9 were considered to have been destroyed by air weapons!
During the Falaise pocket battle the RAF claimed 3.340 soft skinned vehicles and 257 armored ones while the USAAF claimed 2.520 soft and 134 armored vehicles. Yet when No2 ORS examined the area they could only find 133 armored vehicles of which only 33 had been the victim of air attack. The stats were better for unarmored vehicles (cars, trucks, motorcycles) as 325 of 701 were victims of air attack but in both cases there was a chasm between claims and confirmed kills.
Allied fighter bombers were fast and could engage enemy fighters but their speed worked against them in the ground attack role. For those missions a dive bomber would be preferable but neither the USAAF nor the RAF could be convinced to design and use such a plane. Officially the reason given was that such a slow and unmaneuverable plane would not survive in enemy airspace but the real reason was they did not want to spend resources for purely Army missions.
In the field the fighter bombers had a poor record against armored targets. Their guns were moderately accurate but had a low caliber and could not destroy armored vehicles. Their air to ground rockets had more destructive power but they were hopelessly inaccurate. An average Typhoon pilot, firing all eight rockets in a salvo, had roughly a 4% chance of hitting a target the size of a German tank in trials. In the field of battle one would expect this percentage to be even lower.
Against unarmored targets (like trucks) however their performance was more than adequate.
The other major problem of fighter bombers was their limited armor. Unlike the Stuka and the Sturmovik they did not have adequate protection against A/A defenses. For this reason the German anti-aircraft defenses protecting important targets (bridges, supply bases etc) were able to extract a heavy toll on them.
Despite these problems the Western Allies fielded large ground attack forces and these were used extensively in NW Europe. Even though they had serious limitations they certainly had an impact in the fighting. Although they were not a big threat for armored vehicles they did force the Germans to move supplies only at night.
Overall this book is an excellent study of the evolution of RAF and USAAF CAS doctrine and it debunks postwar exaggerations of Allied air support.
Note: In page 31 it is stated about the 1944 campaign in NW Europe: ‘During that campaign the Germans had been able to set up an air warning system against air attack based on the interception of support requests from British Army units.’This is a reference to the German exploitation of the Slidex code system and plaintext traffic.