Barnes Wallis' Tallboy[1] was a 5 ton bomb designed to be dropped from a high altitude and penetrate deep underground. Upon detonation at the correct depth it could create a large crater, up to 100ft deep and 80ft across, which was identified as being useful for attacking railway targets and airstrips, as repair of these craters was time consuming. Combined with the specialised bomb sights used by the squadron who dropped the Tallboys, successfully bombing a small target such as a viaduct or railway line was doable.

However this bomb wasn't used before June '44, when most of the death camps were closed or closing, and the short supply of Tallboys meant that they were exclusively used for targets of high military importance.

1. http://en.wikipedia.org/wiki/Tallboy_%28bomb%29