(UTN/UAS/ATIS) Fusion-Impulse Mass Driver
The FIMD, or Fission Impulse Mass Driver is a weapon system invented in the late 21st century by the Terran Space Research Corporation, that has been in use with the UTN Armed Forces since it's founding, and remains in use with the United Aquarian Systems over 3000 years later.
The weapon utilises a controlled Nuclear Reaction to propel a solid projectile at high velocities. The projectile, often refered to as a "slug", is loaded into the firing chamber, after of which the ignition chamber is filled with a small amount of Nuclear fuel - essentially a 'pellet' of Uranium-235. A high-powered laser is then fired into the fuel pellet, inducing a nuclear reaction, which propels the slug. FIMDs are based on similar principles to firearms of the 20th and 21st centuries, but rather than relying on gas expansion, the slug is propelled by Nuclear energies, and thus achieves a much greater muzzle velocity.
Fission Impulse derived weapons are used by all branches of the UTN Armed Forces, from handheld weapons to the main guns of warships. Despite being many thousands of years old, FIMD based weapons continue to be the primary weapon system, and have been constantly upgraded. The FIMD was replaced by the HMFIMD as the primary weapon of the UTN Navy, though many older warships are still equipped with the FIMD.