As I said before, if you have references, lay them here. I am more than happy to read them.
Meanwhile, here is one of mine :
https://nuke.fas.org/guide/usa/doctrine/dod/fm8-9/1ch3.htm
Here is what he says : "An air burst is an explosion in which a weapon is detonated in air at an altitude below 30 km but at sufficient height that
the fireball does not contact the surface of the earth."
For a 20 Kt bomb, diameter of fireball is at maximum 145 meters in radius (
https://nuclearweaponsedproj.mit.edu/fireball-size-effects). So if detonated at 500 meters+, it will not come in contact with ground.
It was indeed an air-burst.
I can give you more references too, if you like book type of references.
Technically, Little Boy and Fat Man were air bursts in the sense that they did not contact the ground, but that did not make them true air bursts.
Why not? Because of certain requirements...
What airburst physics tells us about nuclear targeting decisions, and why it took so long for the NUKEMAP to support arbitrary burst heights.
blog.nuclearsecrecy.com
...the Target Committee was talking about in May 1945: they wanted to maximize the radius of the 5 psi overpressure range, and they recognized that this involved finding the correct detonation height and knowing the correct yield of the bomb. They knew about the reflection property and in fact referred to the Mach stem explicitly in their discussion. Why 5 psi? Because that is the overpressure used to destroy “soft” targets like the relatively flimsy houses used by Japanese civilians,...
An illustration in the above source explained that '5 psi' requirement. It showed a reflected pressure wave and that pressure wave cannot exist if the detonation is above 'A' altitude and below 'B' altitude. In other words, the bomb had to be technically an air burst but because the detonation is sufficiently close to the ground
WITHOUT TOUCHING THE GROUND, so the burst is called a surface/ground burst.
...you can actually see the reflection of the shockwave in some nuclear testing photography, like this photograph of Shot Grable, the “atomic cannon” test from 1953:
When I was active duty, my first assignment was the F-111E at RAF Upper Heyford. At Heyford, I was once assigned to Victor Alert duty. Victor Alert is when X amount of jets are taken off the weekly sortie list, moved to a guarded area of the base, loaded with nukes, and each jet have a nav cartridge programmed with specific coordinates. The aircrews do not know what those coordinates are until they are given the order to launch, and by 'launch', I mean actually take off. It means the Weapons System Officer (WSO), the guy that sit on the right seat in the cockpit, have permission to plug the nav cartridge into the jet's INS while the pilot, the guy that sit on the left seat, taxi the jet to the runway for take off.
Those F-111Es were loaded with the B61 freefall nuclear bombs. Back then, the B61 was not equipped with GPS guided tail fins for improved accuracy. All F-111 aircrews, E model at RAF Upper Heyford and F model at RAF Lakenheath, trained with the dive-toss technique. The B61 bomb was capable of being air, surface, or contact (ground) detonation programming.
Fuzing | In flight fuzing and yield selection merely by turning a dial. Full fuzing options (FUFO): high or low speed delivery, high altitude or low altitude (release heights as low as 50 ft.). Current mods have five fuzing options:
Free fall air burst (high altitude only)
Parachute retarded airburst (high or medium altitudes)
Free fall contact burst (high or medium altitudes)
Parachute retarded contact burst (high or medium altitudes)
Parachute retarded laydown delayed surface burst (delivery altitudes up to 5000 feet), 31 and 81 sec delays available
The Mod 11 has a special ground impact time delay feature to allow it to penetrate into the earth before detonating.
Delivery accuracy <600 feet. |
See the difference ? With 'air' and 'ground' bursts, there would be no reflected wave effect.
Back in WW II, Fat Man and Little Boy were not air bursts even though they
TECHNICALLY SPEAKING never made contact, so they were considered surface/ground bursts because they had to detonate close enough to the ground, without contact, in order to achieve certain physical requirements.