The different types of military robots can be divided into two general categories based on where they are operated. Unmanned ground vehicles (UGVs) are robots that move around on wheels or tracks. These military robots can perform sentry duties, examine potentially hostile situations, and perform many other widely varied tasks. The other main category is unmanned aerial vehicles (UAVs), which are essentially automated or remotely controlled planes and helicopters. UAVs can have wingspans anywhere from two to over 20 feet (about 0.6 to 6 meters) and are often used for aerial reconnaissance, though some are also equipped with live ordinance that can be used against land or air based targets.
Military robots have been in use since around the second decade of the 20th century, when the first unmanned aircraft was developed. Early military robots also appeared during Second World War, when Germany employed small remotely controlled vehicles known as tracked mines. These tracked mines were some of the first UGVs to appear, though they suffered from weaknesses such as easily destroyed control cables. The Soviet Union also used radio controlled tank UGVs around this time. These teletanks were full sized and could be operated manually if needed.
Modern military robots are used to fill a variety of niches, from reconnaissance to threat assessment. Some of the smallest UGVs that are used for reconnaissance operations are less than a foot (about 0.3 meters) long, and can run on either tracks or wheels. Medium sized UGVs are often used to both locate improvised explosive devices (IEDs) before they can injure human soldiers and enter and assess potentially hostile environments. Some of these robots are also designed to perform more specialized tasks, such as entering hazardous situations to extract injured soldiers. The largest UGVs can be the size of a truck or tank and can perform many of the same roles as manned versions of those vehicles.
The two main functions performed by UAVs are reconnaissance work and the delivery of ordinance. UAVs designed to gather intelligence can vary in size from units that can fit in a backpack to others that are just as large as manned aircraft. Small UAVs are typically used for reconnaissance because they can be carried into the field by soldiers and then sent ahead to assess the situation. Some of these military robots have fixed wings, though others are helicopters. Large UAVs are often used for intelligence gathering as well, though some are also equipped with missiles, bombs, and other weapons systems.