The ground forces have approximately 120,000 men. Their major units consist of eight motorized rifle divisions and five tank brigades. There are also various smaller special purpose units and support organizations. The forces are distributed among three territorial commands having headquarters at Sofia, Plovdiv, and Sliven. The division is the basic organizational unit in Warsaw Pact combat forces and has about 10,000 men. Five of Bulgaria's divisions are believed to be near combat strength, but three probably have only skeletal strengths and would be built up with the mobilization that would accompany a major national emergency. Each of the other Warsaw Pact armies has a number of tank divisions. The fact that Bulgaria has only tank brigades, which are probably one-half or less the strength of divisions, reflects the austerity of its armed forces. Motorized rifle divisions have one tank regiment, one artillery regiment, and three motorized rifle regiments. The tank brigades, because they are smaller, probably have fewer tanks than the motorized rifle divisions. Most of the tanks used by the Bulgarian army are the early post-World War II model T-54. There are some newer models in the inventory, and a few of the older World War II T-34s are still being retained. Artillery pieces include guns and gun-howitzers from 82 mm to 152 mm, antitank weapons up to 100 mm, and small antiaircraft guns. Some units are equipped with short-range missiles and unguided rockets. There are enough personnel carriers or self-propelled weapons so that all men in a unit can be transported simultaneously. Air and Air Defense Forces The air and air defense forces have approximately 20,000 men, 250 combat aircraft, an assortment of antiaircraft guns, a few surface-to-air missiles, and a modest quantity of air defense radar and communications equipment. Combat aircraft are organized in squadrons, usually with twelve airplanes each. In 1973 there were six fighter-bomber, twelve fighter-interceptor, and three reconnaissance squadrons. The fighter-bomber squadrons use the MiG-17, an aircraft that is obsolescent but that performs well in a ground support role. About one-half of the fighter-interceptors are also MiG-17s, but three of the interceptor squadrons have the newer MiG-21. The only bomber aircraft in the air forces is the near-obsolete Il-28. The Il-28 squadron has a reconnaissance role. A few old cargo or passenger planes provide a minimal transport capability, but there are about forty helicopters that can perform shorter range personnel and transport functions. Air defense forces are positioned to provide protection for the country's periphery as well as for a few cities and air installations. Ground and naval forces have antiaircraft weapons to defend their own units. Early warning radars are located mainly along southern and western borders, and their communications lines are presumably linked with the Warsaw Pact air defense warning network.