  It is scientifically and technically possible to build an earth penetrating
device that could bury a B61-7 warhead 30 meters into concrete, or 150 meters
into earth, before detonating it. The device (based on knowledge and technology
that are available since 50 years) would however be large and cumbersome.
Better penetrator materials, components able to withstand larger stresses,
higher impact velocities, and/or high-explosive driven penetration aids, can
only marginally improve the device. It is concluded that the robust nuclear
earth penetrator (RNEP) program may be as much motivated by the development of
new technology directly applicable to next generation nuclear weapons, and by
the political necessity to periodically reassess the role and utility of
nuclear weapons, than by the perceived military need for a weapon able to
destroy deeply buried targets.
