The Micro Quantum Torpedo was introduced to help arm the relatively small and undefended Starfleet Runabouts. Although Runabouts were equipped with Phaser arrays, a more powerful weapon was required to help defend the Runabouts against larger, more powerful opponents such as the Dominion fighters they were frequently encountering. Measuring just 13 cm in length, the Micro Quantum Torpedo is the most powerful weapon of it's size. When fired from a Runabout, the torpedo incorporates a mini guidance system which will home in on the nearest enemy target, but this guidance system does not kick in until 3.7 seconds after it is launched in order to let it clear the vicinity of the Runabout. As with all torpedoes, the Micro Quantum Torpedo can be fired while the ship is at Warp.
Torpedoes are the heavy weapons of any fleet - tactically advantageous both in their explosive output and the fact that they can be fired while the vessel is traveling at warp, the torpedo has been in service within the federation for almost as long as the phaser beams. Torpedoes are at a disadvantage against maneuverable targets however because they can not be fired in any specific direction other than the direction the vessel happens to eb facing at the time. Torpedoes have limited guidance systems to compensate for this though.