A recently developed class of firearm is the personal defense weapon or PDW, which is in simplest terms a submachine gun designed to fire ammunitions with ballistic performance similar to rifle cartridges. While a submachine gun is desirable for its compact size and ammunition capacity, its pistol cartridges lack the penetrating capability of a rifle round. Conversely, rifle bullets can pierce light armor and are easier to shoot accurately, but even a carbine such as the Colt M4 is larger and/or longer than a submachine gun, making it harder to maneuver in close quarters. The solution many firearms manufacturers have presented is a weapon resembling a submachine gun in size and general configuration, but which fires a higher-powered armor-penetrating round (often specially designed for the weapon), thus combining the advantages of a carbine and submachine gun. This also earned the PDWs an infrequently used nickname — the submachine carbines. The FN P90 and Heckler & Koch MP7 are most famous examples of PDWs.