So the Hot New Argument is of course whether or not the U.S. is actually seriously considering using nuclear penetrators to go after the Iranian nuclear (enrichment?) facility at
Natanz. Arguments over how much cover the facility has (twenty meters? Seventy-five meters? Five meters? Measured from the floor? The ceiling?) and over what type of cover (bored?
Cut and cover? Rock?
Shale? Soil and broken rock?) are the rage. An enormous conventional explosion test named
Divine Strake is planned for this summer at the
Nevada Test Site. This has gotten many panties in twists about the legality, morality, and desirability of the U.S. pursing nuclear earth-penetrating weaponry - either the development, testing, deployment or use thereof.
Which begs the question, what else do you use?
One method which has been mentioned several times is the 'multiple bomb' technique. This has much to recommend it, in my opinion. Unlike 'global thermonuclear war' scenarios, where the use of nuc penetrators might in fact be a relatively scaled response, when going up against a developing nuclear power I am firmly in the 'this is a bad, bad, BAD idea' camp. While it's true that 'carpet bombing' is not likely to be very effective, recent technological developments offer an alternative.
I'm not talking about smart bombs per se. Those are seeking weapons, and there will be no designator signal available for them to home on - even if there was, it would be a near-impossible task to hold such a designator on a spot steady enough to produce the 'multiple strike excavation' required. Furthermore, scene-matching or target-recognition will be complicated by the fact that after the first bomb hits, the scene will of course be unpredictably (and dramatically) changed - at least enough to deny subsequent targeting systems accurate enough fixes.
However, competent munitions - in other words, navigating weapons - would be just the ticket. Typical U.S. gravity bombs can be coupled with a navigating tailkit and tail-mounted fuze for cratering use; the bomb itself costs approximately $4,200.00 and the guidance/fusing units in the low tens of thousands. While a 2,000 lb. bomb does not produce a very deep crater - feet, perhaps - the use of DGPS guided tailkits could quite possibly drop successive bombs within a quite small CEP - probably well within the crater size. Given that the U.S. has plenty of time to go about this, what's to stop us simply hammering away at the same spot with these weapons?
There are many advantages. Collateral damage is hugely minimized compared to the ridiculous use of a high energy weapon. No matter what the politicians tell you, this is a nuclear weapon. This will not be like an 'underground nuclear test' where the device is placed carefully in a hole drilled several hundred feet into the earth, then sealed in, and detonated. No matter what, there is a chance of weapon failure; of the breach of the physics package at the surface or above it; of insufficient penetration and detonation in atmosphere. Think about that for a moment. Even if everything works except for the fact that it doesn't quite go that deep - and remember, they're trying to find out if it will reach seventy five feet, when test site tunnels are much, much deeper than that - then you have an atomic detonation. In the atmosphere. On a foreign sovereign nation.
The United States has just used atomic weapons on someone's country.
We haven't 'destroyed a nuclear facility using a contained explosion.' We haven't 'prevented another country from irresponsibly gaining nuclear weapons.' We have attacked another nation with atomic weapons.
Back to the point. Using our multiple conventional strike method would not only reduce the political fallout (har de har) of the attack, but demonstrating the capability would, in itself, possibly increase the demonstrated sincerity of threats made (explicit or implied) in any negotiations prior to violence. If the only way to get to said underground bunkers is via nuclear weapons, it is far more likely for the owners of the bunker to convince themselves that the U.S. would never perform a first strike, and hence adopt a harder position in any interaction - one which might (especially given the current administration's, um, lack of grounding in reality) drive the U.S. side to actually decide it had no choice. On the other hand, if it was clear that the U.S. did have options for direct unilateral action which didn't carry anywhere near the penalty associated with first use of nuclear weapons - after all, a conventional strike on another country's roundly condemned nuclear program is an old tradition by now, see Osirak - then they might pause if the U.S. adopted a hard line.
The Gravity Bomb Tapdance method is also much, much cheaper. At $4,200 per bomb unit and let's say $50,000 per navigation kit, even if you decided to throw a hundred bombs at the target, you're still only in $5,420,000. I'm not sure what a B61 warhead costs, but I know it probably has on the order of six to eight kilograms of Pu-239 in it. You do the math. A Tomahawk strike? The newest, cheapest Tomahawkcruise missiles (which don't penetrate the ground) cost around $750,000 each.
You could minimize the number of sorties required to produce this effect, as well. A B-52H Stratofortress, which can drop the Mk.84 LDGP bomb, can carry 45 of them using the HSAB wing mounts as well as internal load. So two B-52 missions could drop 90 weapons. One design study I would love to see is if there is enough excess energy in the profile of a Mk. 84 to allow the attachment of retarding kits and ballutes to the rear of some of the weapons in the loadout, and then to simply drop the entire stick and have the navigation systems fly varying arcs so as to produce staggered 'time on target' arrivals. If the first weapons released went for maximum glide, and the later ones went for maximum retard, then dropped the retarders while still at altitude in order to gain velocity, it might be possible?
Anyway. Ideally, you would be able to just upload a target coordinate to all the weapons in a BUFF loadout at once, and then simply pickle the entire load. Weapons would arrive in quick succession. For maximum cratering effect, in addition to tail-mounting the fuzes, some basic case hardening work might be done on the bombs themselves; perhaps strengthen the noses. After all, the British built purely gravity bombs in World War Two (the 'Tallboy') that broke the sound barrier, and penetrated up to a hundred feet of soil before exploding. Those weapons weighed approximately six tons, and were dropped from only fifteen to twenty thousand feet from Avro Lancasters (by the famed 617 squadron, originally on the U-Boat pens in France, later on the V-3 supergun system and other targets).
If you wanted to sex up the idea more, and actually build new weapons, then the first thing I would do is take a look at the French Durandal cratering munition. This weapon, designed to be dropped at low altitude against runways, was intended to be 'lobbed' upwards slightly by a fighter/bomber...at which point it would tip over and fire a short-lived but powerful booster rocket to give itself downwards vector and slam through the runway surface before detonating. Perhaps you could design a new Mk. 80 tailkit that had the DGPS navigation system and a final-seconds booster - once the weapon was within say a hundred feet of its target ground point, and knew it was on profile, it could ignite the booster. That might give it another few feet of penetration before detonation. The good part is that that could possibly be just added to a tailkit system as well.
In any case, it's quite possible there are massive holes in this idea, which is not original...I just played with it a bit. Some colleagues and I have been tossing that one around ever since Gulf War I and the 'Hardened Penetrator Weapons' that were ginned up for the command and control bunkers, and we sure weren't the only ones who were playing with it.
Maybe I should do some math...I used to have some data on Mk. 84 cratering effects somewhere, damn it. Where's my copy of GWAPS?