New Bomb Drills for Bunkers

Weapons Grade author David Hambling has another fascinating two-part series for Defense Tech, on weapons that drill and scrape their way through targets.
Meet Deep Digger, first of a revolutionary new generation of bunker-busting weapons, described in this weeks New Scientist. This is literally ground-breaking new technology which uses cannon to tunnel through solid rock, drilling a channel for the bomb.
Existing weapons for attacking hard targets are kinetic, relying on sheer momentum to break through rock and concrete. To get much improvement you have to make them much bigger - like the outsize 30,000 lb Massive Ordnance Penetrator, or much faster - like the proposed conventional version of the D5 Trident ballistic missile, or denser - like the heavy BLU-109 with its ballast of dense metal. But you cant get around the laws of physics. As Princeton's Robert Nelson points out in a very thorough analysis, even if the penetrator is a hypersonic projectile made of solid depleted uranium:
no Earth Penetrating Weapon can penetrate reinforced concrete deeper than four times the length of the missile.
So this approach really isnt going to get you more than a hundred feet through rock at best, and the practical limit is much less.
The supercavitating bunker-buster I revealed last year looks neat, but the jury is still out on whether it works. A lot of people in the industry simply dont believe that it can. The Broach is an interesting idea but limited to a few metres.
Deep Digger is different. It does not depend on the kinetic energy of the warhead at all in fact, it parachutes down. Then it stars drilling. The weapon is limited only by how deep the drilling process can go, which is a matter of how deep it can muck (clear debris from the shaft). And although the details are classified, that is much, much deeper than any kinetic weapon will ever go. In the tests last year, it demonstrated a tunneled down ten meters -- about 50% more than the BLU-113, which is the current record holder.
It has numerous other advantages. One is a thinner casing which means more payload. Another is that it does not undergo a shattering 10,000g impact. Other penetrating bombs need special insensitive explosives; Deep Digger can carry a range of warheads, as well as sensors and communications. It can stay in touch with the launch aircraft and report its progress; multiple Deep Diggers could be co-ordinated to detonate simultaneously producing a combined shockwave.
Part of the secret is the rock-breaking projectile, developed like the cannon at ARDEC, the US Armys Armament Research Development and Engineering Center at Picatinny. David Burns, the Program Manager, describes it as being a special .75 calibre round, a monolithic design which is more robust and performs better than earlier projectiles. In place of the blasting gel used earlier it now employs a solid high explosive called PAX-11, one of Picatinnys own special recipes.
Deep Digger has already moved on from the version described in this presentation. Burns is confident that its proven ability to drill consistently through rock will make Deep Digger the leader in its field.
It doesnt stop with bombs either. There are some other interesting applications for Deep Digger technology too, which well be looking at in part two of this little series, starting with a breaching cannon that cuts through brick walls like a chainsaw through plywood.
-- David Hambling