Frigates are swift, flexible warships. Unlike larger vessels, they are able to land on planets. Although lightly armed, Alliance frigates usually carry a squad of marines for security and groundside duty.
The most important role filled by frigates is scouting and reconnaissance. Thanks to mass effect technology, ships and communications can travel faster than the speed of light. Sensors, however, are limited to the speed of light. If an enemy ship is a light year away, a stationary observer will only be able to see it when its light arrives in a year.
An attacker will always gain surprise against a defender; attacking ships moving faster than light will arrive long before their light speed-limited sensor data does. For defense, fleets are surrounded by spheres of scouting frigates. These vessels detect enemy ships passing by them, and transmit warnings to the main body. The Normandy is a prototype "deep scout" frigate, developed by the Systems Alliance with the assistance of the Citadel Council. It is optimized for solo reconnaissance missions deep within unstable regions, using state-of-the-art stealth technology.
For centuries, it was assumed that starship stealth was impossible. The heat generated by routine shipboard operations is easily detectable against the absolute-zero background temperature of space. The Normandy, however, is able to temporarily "store" this heat in lithium heat sinks deep within the hull. Combined with refrigeration of the exterior hull, the ship can travel undetected for hours, or drift passively for days of covert observation. This is not without risk. The stored heat must eventually be radiated, or it will build up to levels capable of cooking the crew alive.
Another component of the stealth system is the Normandys revolutionary Tantalus drive, a mass effect core twice the standard size. The Tantalus drive generates mass concentrations that the Normandy "falls into", allowing it to move without the use of heat-emitting thrusters. The heat sink and Tantalus drive systems allow the Normandy to loiter undetected in an enemy system to monitor traffic, or drop infiltration teams on enemy worlds. Should the Normandys design prove useful in field tests, it is expected that a follow-up class incorporating "lessons learned" will be produced.