Even worse than air attack would be artillery. The Japanese and Russians were particularly good at plastering their enemies with lots of artillery fire. At least you can shoot back at planes; artillery shells just come down without any chance of stopping them. Being an artilleryman (at least formerly) I can attest to the noise that shells landing with the characteristic CRUMP can make - and that was at a distance. There were mortar and rockets landing near (relatively - the closest was about 75 meters away) to us in Iraq and that was pretty unnerving. It makes me think of the scene in Band of Brothers where they were getting shelled by the 88's and many of those guys were injured.
I'm lucky to be able to say I don't know what those guys (to include our dear Roque, et al.) went through in WWII. Artillery and air strikes meant even being a REMF (which is more of a Viet Nam acronym I suppose) in Anzio wasn't safe!