Maj. Gen. Gary L. Curtin, USAF, is director of the Defense Special Weapons Agency (formerly Defense Nuclear Agency). George W. Ullrich is DSWA’s civilian deputy director. On July 16, 1997, they addressed the Defense Writers Group in Washington.
New Cave Dwellers
Curtin: “Hardened and deeply buried targets have evolved over the years as one of the lessons of Desert Storm. A lot of the people who are involved in either the proliferation of weapons of mass destruction or in wanting to protect command-and-control facilities have migrated into making their facilities harder and harder.
“The old ‘cut-and-cover’ kinds of targets we saw in Desert Storm—and which we were really pretty successful at destroying—were perceived as no longer hard enough, so building things into mountains has become the way to preserve the things that are most important to you. We have witnessed that in Korea for many years. We have witnessed it in a lot of other places in the world. …
“These are very difficult targets, and the idea of being able to destroy them totally was principally in the past focused on nuclear weapons. But nuclear weapons are basically not … acceptable … for most cases, so we have to look at alternatives.”
Targets in Two Flavors
Ullrich: “In the cut-and-cover kind of facility, … you basically dig a hole and build a concrete bunker, and you cover it. And then, there are tunnels. They are really two very distinct targets.
“For the cut-and-cover type, there is no question that conventional munitions can be designed. It’s always a measurement of who’s ahead. You can go deeper, but there’s a cost of going deeper. There is also a cost to trying to get a better penetrator. …
“However, tunnel facilities pose a challenge in and of themselves. That’s a much more difficult target to deal with. In fact, there are some targets where even nuclear weapons are challenged by these kinds of facilities, if they are sufficiently deep. So that group truly requires a different approach.”
Of Tunnels and Tributaries
Ullrich: “Now, there are subclasses of tunnels. There are what we call the simple tunnels and very complex tunnels. The simple tunnels are basically tunnels that are used, say, to park Scuds [missiles], and you require ingress and egress. That’s the primary function, to protect the system, but the system has to come out to do its work. … You deal with impeding ingress and egress.
“With facilities that are designed to be buttoned up, it’s a more difficult challenge, but there’s no facility that doesn’t require some sort of umbilicals, and over the long term, you can’t isolate yourself from the rest of the environment and from power sources, water sources, and so forth. There are other functions that can potentially be attacked and disrupted.”
Curtin: “What we are focusing on is not trying to blast them [the targets] into oblivion but rather something we call ‘functional kill.’ Functional kill is the ability to go after the specific system or systems in a facility that you can shut down and in doing so put it off line for a period of time but not forever.
“You want to do something that will keep it from doing what it’s supposed to do for a specified period. That can require, for example, going after power, after communications, after ventilation—things like that which you might be able to access, or some portion.
“So, understanding underground facilities, and then applying the current technologies of weapons—which are, surprisingly, better than you might imagine, in terms of penetrating into rock, detonating, and causing damage—is where we are working today. We have been using some of the facilities … at the Nevada test site, underground tunnels, and the tunnelling capability that we have out there, to test and demonstrate the effects of high explosives on tunnels, and are working to find different ways to attack tunnel facilities. The program is still under way. There’s no conclusion that I can give to you. We’re making some progress.”
Curtin: “The Air Force has something called the Advanced Unitary Penetrator, which is a narrower weapon, harder, designed to penetrate deeply into rock and other kinds of material. It shows a lot of promise.
“You couple that with the hard target smart fuze. It has a number of modes. One is what they call a ‘path length’ mode, which measures the distance it travels in an object. We also have the ability, with that fuze, for it to count the number of voids it passes through. It has a timing option as well. So it’s a very flexible fuze, … and it will be part of future weapons. It will allow us to more specifically go after targets and then to destroy them with the penetration into the area.
“The charge itself [in the Air Force’s AUP] is small, but when you’re talking underground, you don’t need a large charge. If you can get the charge down to the target point, then a small charge in a confined space does a tremendous amount of damage.”
Curtin: “Against a wide variety of targets, precisely aimed and accurately delivered conventional weapons will do the job that, many years ago, we only thought could be done with nuclear weapons. I think there is certainly a capability to take on very difficult targets today that we couldn’t have done in the past with anything less than nuclear weapons.”
Ullrich: “It [the AUP] would have roughly the capabilities of the [Air Force] GBU-28, but it sits in a much smaller package. … It [the weapon’s potential attack depth] depends. It could be a hundred feet in soil, but with rock and reinforced concrete, you’re probably talking tens, a few tens of feet.”
Curtin: “We’re talking granite and reinforced concrete as the kind of obstacle that you’re throwing these things against, and those are very difficult to penetrate. … The AUP will go further than [12 feet], but, again, it depends on the composition of the material. And if you’re talking reinforced concrete, it depends on how reinforced it is. There are just a lot of variables involved. It’s designed to go further than 12 feet. I can’t give you specific depths, obviously, because that just means the other guy will build them [hardened targets] deeper.”
Ullrich: “If you’re looking for large-area structural defeat [of a hardened tunnel target], which is sort of the metric from the old nuclear targeting days, then no, you can’t do that [with conventional arms]. But every one of these facilities has probably a collection of Achilles’ heels. Now, if you have the capability to assess the functionality, the locality, through sophisticated sensor technologies, there is hope in applying some conventional insults that would disrupt that facility.”
Curtin: “You have to break lock with the idea that you’re smashing a facility. That’s not the right answer. That’s why the functional-kill approach—to go after entrances, or the pad outside for the launcher, or something like that—is used to achieve the same thing.”
Chemical, Bio Sensors
Curtin: “We are working programs with other organizations, including Sandia Corp., for unattended ground sensors that could be deployed around a suspected facility to provide monitoring over a period of time to try to detect the proper signatures that would allow you to characterize the facility itself.
“The biggest problem with underground tunnel facilities is intelligence. You can’t, over time, as you would with a cut-and-cover facility, see them build it. All you’re seeing is the entrance and the spoil coming out. You don’t necessarily know where the path is inside. Short of having the blueprints, you have to find some other way to characterize it.
“That is a real challenge for … human intelligence. … It’s also a challenge to find sensors that will add to that information and allow you to characterize it sufficiently so that you can do this functional-kill operation. … We’re talking seismic sensors. We’re talking electrical sensors. There is a variety of different sensors that you can put out there to try to detect either emissions or vibrations or other things from the facility itself.”
Catching the Cloud
Curtin: [Our goal is] “to provide the warfighter with the necessary planning tools and then the weapons and tactics [to prevent the postattack spread of WMD toxins]. The planning tools allow you to understand the facility and know where to put the weapon precisely to close it down. We have done testing with simulants to allow us to know what’s coming out, and we’ve worked different kinds of tactics.
“In the cut-and-cover facility, the idea is to collapse the facility in on the material inside by setting off the charge beneath the floor, so that you don’t just blast up into the air. This has proven to be a very effective technique to dramatically cut back on the emission of any products inside.
“We have also been working with the services on other techniques to try to nullify what might be inside to keep it from causing any damage even if it does come out.”
Tracking Airborne Poisons
Curtin: “We have worked prediction models and have tested and demonstrated them, so we understand pretty well what comes out of a point source, if you in fact strike it, and how much of that will propagate, and where it will go, and we can then alert people downwind if there is in fact any hazard. We put together a package of things that allows the warfighter to do much more than he could in the past.”
Ullrich: “These facilities are often fairly large. … One of the difficulties is: How do you distribute the damage to one of these facilities? We are looking at some so-called advanced payloads. At this point it is very preliminary. The prospect for using, say, incendiary-type warheads or other warheads that would distribute the energy better and for a longer period of time. … Fuel-air [explosive], per se, doesn’t work that well on the ground, we believe, but there are other techniques using thermites or other payloads that might offer some advantage.
“Of course, the key here is that you want to have the high-temperature environment to neutralize potential agents [over a period of time.] They would have to reside in that thermal environment for a period of seconds to minutes.”
Weapon Development Effort
Ullrich: “We are about to embark on Counterproliferation ACTD II—CP II as it’s called—that will in fact demonstrate this Advanced Unitary Penetrator. Should it appear very promising, one could probably develop a few prototypes under that program and then get into some quick development program, but I think it’s premature at this point. That [effort], by the way, will carry on for about another two years. At that point, we’ll at least have an assessment of whether that concept is worthy of pursuit.”
Curtin: “And the AUP is not specifically focused on the tunnel targets. It’s more focused on the hardened, shallow-buried targets … where you have to go through a lot of reinforced concrete as opposed to going into granite or something like that.”
The Tyranny of Physics
Ullrich: “You’re dealing with fundamental material parameters here. … There is a limit to how deep you can get with a conventional unitary penetrator. There is some improved penetration with fragments and rods, and a lot of R&D has gone on in the past, but fundamentally, you’re not going to come up with a magic solution to get 100 feet or deeper in rock.
“If you go to higher velocities, you reach a fundamental material limit where … the penetrator will eat itself up in the process, and in fact that will achieve less penetration than at lower velocity. So you get into these different regimes where you are really just fundamentally limited, physically, in how deep you can get into rock.
“What’s left, then, is to deal with the energy package that you have on board [the weapon]. The B-61 nuclear penetrator is intended to have a substantial kill capability against these kinds of targets. Conventionally, if you’re set on structural damage to these targets, I think you’re going to be very disappointed.
“The conventional solution has got to focus on these functional defeat mechanisms. … We’ve looked at shaped charge, two-staged-type weapons. Boosted penetrators and a variety of options. These experimental concepts have been explored. Even with those, it’s an incremental gain. You can always find a mountain that’s going to go a lot deeper than the weapon.”