Tactical UAVs were developed for the ground and maritime force delivering near-real-time imagery up to 200 kilimeters. These operational assets are based at Fort Hood and have been deployed to Kosovo under KFOR.
Medium altitude endurance UAV such as the Predator provides intelligence to theatre commanders out to ranges of 500+ kilometers.
High altitude endurance UAV (Global Hawk) are designed for long range wide-area surveillance for long sensor dwell over a target area.
Unmanned Underwater Vehicles will be launched and return to their mother ship, providing submarines with over the horizon organic capabilities
Other elements are required to make UAVs feasible in the global battle space. The tactical control station (TCS) is the software and communication links required to control the the various UAVs, providing C4I connectivity with other systems.
Some famous UAVs include:
X-47B, Northrop Grumman are capable of taking off and landing on aircraft carriers and be capable at long-range surveillance and stealth survivability with added features such as aerial refueling.
Canadian Force in Afghanistan use their own version of a UAV, the video below goes through a detail review of its use.
British MQ-9 Reaper and Predator B