To begin with, when the air campaign ahead of Operation Husky (the campaign that culminated with the invasion of Sicily) began, the Allies already had a significant numerical superiority over the Axis air forces in the theatre:
Operation HUSKY air planners had nearly 5,000 operational aircraft at their disposal compared to the 1,500–1,600 Axis aircraft based in Sardinia, Sicily, and southern Italy.
Once the campaign in North Africa was over, after the final defeat of Axis forces in Tunisia, the Allies began strategic bombing of targets in Sardinia, Sicily and the south of the Italian mainland. These targets included all the principal airfields available to Axis air forces in those areas. The principal targets of the Northwest African Air Forces (NAAF) in Sicily are shown below:
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- Image source Wikipedia
Another preliminary objective prior to the invasion was to secure forward bases for allied air forces. Long-range bombers were operating from bases in north Africa, but the operational range of allied fighters was much less. Malta was already held by the Allies, despite having been subject to a long-term siege by the Axis naval and air forces.
To supplement these positions, Operation Corkscrew was executed with the objective of capturing the island of Pantelleria, which lies almost equidistant from Tunisia and Sicily:
The acquisition of the airfields in Pantelleria ... was the critical first step to acquiring the necessary basing for fighter support for further operations northward in the Mediterranean.
Axis troops on Pantelleria surrendered on 11 June, with the smaller islands of Lampedusa and Linosa to the south of Pantelleria falling on 13 June, and the island of Lampione on 14 June.
Thus, while Axis air forces had largely been driven off Sicily by Allied bombing raids (by 10 July, only two of the nineteen airfields in Sicily remained fully operational, and more than half the Axis aircraft had been withdrawn), the Allies now had forward bases from which fighters could operate in support of the landings. These islands served the function of aircraft carriers for Allied air forces, and had the advantage of being much harder to sink!
Operations from these islands were combined with continued bombing operations launched from bases in North Africa.
As a result, the Allies were able to operate with almost complete air superiority. The report Lessons From The Sicilian Campaign compiled immediately after the conclusion of Operation Husky concluded:
Except during the initial landing phase, the enemy air activity was almost negligible. This fact, in connection with the limited road net which was used to capacity because of the prevailing terrain, played an important part in the rapid and successful advance of our forces.
- Lessons From The Sicilian Campaign
An article in Warfare Magazine, titled Allied air power lays the foundation for the conquest of Sicily emphasises the scale of Allied dominance in the air at the start of the invasion:
On 9/10 July the night and morning of the invasion, the Luftwaffe could manage no more than 300 sorties by all aircraft. In the three days 10-12 July, the Desert Air Force alone exceeded 3,000 sorties. ...
By the middle of July the Luftwaffe was restricted to only 25 aircraft based in Sicily. In comparison at 30 July the Allies were operating 40 squadrons from 21 airfields on the island.
On 17 August the last of the Axis forces retreated across the Straits of Messina to the toe of Italy