I really wonder what Michael Wittman thinks, wherever he is, about rockets or bombs not being effective against heavy tanks.
Flat out, a 500 lb egg landing next to a Tiger will likely stun/injure the crew from the shock and resulting bodies thrown against hard metal and render it combat ineffective. It will also likely throw a track and damage the running gear.
An egg or cannon / MG shells setting fire to an "external fuel tank" as some have suggested will likely catch the tank itself on fire, and result in a destroyed vehicle. In case you are not aware, sustained heat of the magnitude of a fire will turn the armour brittle with no chance of repair.
A 1000 lb egg hitting near a heavy tank is likely going to kill the crew from the shock and split weld seams, and make the tank so heavily damaged that it will likely be abandoned. A direct hit is likely going to go through, or have we forgotten about inertia.
I have studied and read extensively on WW2 armour. While I am not an expert, I do retore aircraft and vehicles. I even sat in a Tiger that was abandoned in a foreign country and sits there to this day (can not get an import permit for it). The hardness you guys claim of these vehicles is just not the case.
All in all, heavy tanks were very vulnerable to air power. If they were not, the allies would never have been able to win at Normandy, because it was the incessant allied attacks during good weather that kept the German Armour at bay. They, the German Armour, faired very well at Normandy when the weather prohibited the jabos from finding their tanks.
I will say a supportive thing for the pro armour guys here though. The US halftracks should not stop ANY round in here short of a 7.9mm fired from 500 yds. The armour is 1/4 inch thick on the whole of the vehicle with the exception being 1/2 inch think armour for the drivers FWD windscreen cover. The only other US halftracks with thicker armour were the International Harvester manufactured M5 and M9 series with 5/16 inch armour, which has homogenous steel (welded together) and not face hardened like the 1/4 inch armour on the White and Autocar versions.