PDWs are not specifically a class of firearm, but rather a philosophy of design within firearms. PDW are for defence, in a personal or military circumstance, and are therefore designed with the mindset of quick and simple deployment with a light weight and short overall length. A long, heavy barrel is not needed as a long-range pre-emptive attack is not what it is designed for. Notable examples of PDW include FN Herstall's P90 and MAGPUL's PDW prototype, which featured the same MO as an M4 as it was to be marketed to the US military as a replacement for the M4 in vehicle based squads.