Bunker-busting nuclear weapons are a proposed type of nuclear weapon that would be designed to penetrate into soil, rock or concrete to deliver a low-yield nuclear warhead. These weapons would be used to destroy hardened, underground military bunkers buried deep in the ground usually under 25 to 100 meters or more of concrete. These weapons would in theory limit the amount of radioactive nuclear fallout by confining the explosion underground.

Some have argued in peer-reviewed journals that even a low yield underground blast would at least shoot fallout through its entry hole (Roman candle-style), contaminate water supplies for centuries and if detonated beneath a highly populated area would lead to tens of thousands of eventual deaths. Others state that it is not possible to even conceive of a missile that could pass more than four times its own length through reinforced concrete.

Advocates of these earth penetrating "mini-nukes" counter that the lack of current technology does not negate its possible future feasibilty. They go on to say that underground explosions are effectively an order of magnitude more powerful than an air burst due to the increased ability of solids to transmit shock. Even so, say detractors, the inability of these weapons to penetrate past the measured upper limit of 30 times their length in soil, will necessitate yields in the 3-kiloton range, which - given the shallow depth - would result in crater formation and the release of fallout -- thus negating their perceived increased safety.

During the 2003 Invasion of Iraq and 2001 Attack on Afghanistan, new discussion was generated about such weapons as military commanders became frustrated with their inability to hit hardened, deep targets. These weapons were then (and are now) referred to as the Robust Nuclear Earth Penetrator or RNEP. As part of the USAF Advanced Concepts program for FY2003, significant monies (US$15M) had been allocated for research into these weapons. Again, questions about the feasibility and utility of the weapons came up, and none have been deployed.