air cover 
noun [mass noun]
Protection by aircraft for land-based or naval operations in war situations: they provide air cover for United Nations convoys of relief supplies...
- Undeterred, he continued flying, until he finally broke his back, as a wing commander, while providing air cover for the assault on Arnhem.
- It is no good having all the tanks serviceable if the force cannot get enough aircraft armed and ready to provide air cover.
- Providing air cover for the Operation Jubilee raid on Dieppe, France, on 19 August 1942 was the only time the three Eagle Squadrons operated together.