A munition, such as a warhead, includes a penetrator casing for penetrating hard targets, such as a fortification or reinforced building or other structure, with the penetrator casing having reduced-thickness portions. The reduced-thickness portions provide weak points to the casing that facilitate the casing being transformed into fragments of a desired size/quantity when an explosive within the casing is detonated after the penetration occurs, thus enhancing the effectiveness of the munition. In addition, the warhead may have lethality-enhancing materials, such as additional fragments and/or energetic materials, at the reduced-thickness portions of the penetrator casing. The reduced-thickness portions may be holes, such as longitudinal holes, in the casing, or may be grooves on an inner and/or outer surface of the casing. The munition may be a dual-use munition, with the explosive able to be detonated at a burst height for use of the warhead as a non-penetrating area fragmentation weapon.