Free electron lasers (FEL's) are devices used worldwide for several purposes. In the military, especially in the Navy, they can be used for self-defense against missiles, and small boats. Installed on a ship, an FEL represents a multi-mission, deep magazine, long range weapon. This thesis will describe briefly the basic components and principles of operation. It also explores, by simulations, the effects of changing some of the parameters that generate the laser beam.