Someone correct me. According to everything I have read, the USA does have massive bunker busting bombs and the B2 stealth aircraft to deliver them. But they can not be put on a missile and they are dropped from the B-2 and use gravity and GPS to guide to their target. My question is, if they are indeed gravity driven once dropped, wouldn't the Iranians be able to detect it dropping from the plane and using simple aircraft defense shoot it down considering how slow it would take only using gravity? Especially considering the size they are or do the bunker busters have stealth themselves?
Bunker busters bombs don't really destroy bunkers as it is implied. Most of their weight is in steel so the kinetic energy buries them deep enough to do significant damage. There's very little explosive compared to conventional ordinance so the damage is limited.
What they do excel at is killing everyone inside due to pressure wave in contained space and for that you don't need much of a bang. 20g of explosive is enough to kill everyone in a tank and 50g enough to kill everyone in a room. They run dual or more fuses to ensure ignition but even that is not 100% granted as sometimes the case splits, bomb shifts and shears and so on because the geology of ground isn't consistent and it always lands at an angle to the ground.
If an attack were to occur it would be after all AA + launchers is gone and bombers would be flown with ECM and radar jamming escort.
Radar signature from these older birds is immense enough that you can blind fire an active radar self-guided missile in general area and you will score a hit. Newer ones even have 40km range thermal sensors so that plane that has thermal signature of a sun is just a big target.
GPS is going to be jammed near objects of interest so you can't rely on that so the bomb has to be laser guided. You can technically shoot it down but it's more cost effective to hit the plane with same missile and bring both down.
I would assume that newer bombs are rocket assisted, so that gives them a mach 3 velocity and about 100m of penetration in dirt and about 40-50 of weathered rock or 20m of granite and high strength reinforced concrete.
Ironically iranian missiles would give better penetration than an air drop, but you reach into explosives self detonating on impact at above M2 velocities and you require special compositions to avoid it, which bring yield down.
While US definitely has these weapons, demonstrating them on a shithole just brings unwanted attention from China and Ru which will then study their defense options.
For all practical purposes. Military installation that is 100m underground is only vulnerable to a MT class devices.
For 400m deep installation of significant importance you would go in with multiple MT yield weapons and drop them one after another into the hole previous one created and that would still require at least 5 or more strikes as quality of rock increases deeper you go.
