Domestic defence is the responsibility of the all-volunteer Bulgarian armed forces, composed of land forces, navy and an air force. The land forces consist of two mechanized brigades and eight independent regiments and battalions; the air force operates 106 aircraft and air defence systems in six air bases, and the navy operates various ships, helicopters and coastal defence weapons. Active troops dwindled from 152,000 in 1988 to 31,300 in 2017, supplemented by 3,000 reservists and 16,000 paramilitary. Inventory is mostly made up of Soviet equipment like Mikoyan MiG-29 and Sukhoi Su-25 jets, S-300PT air defence systems and SS-21 Scarab short-range ballistic missiles.