Six months' military service is compulsory for males. Algeria's armed forces in 2000 totaled 120,000 personnel. The army had 105,000 officers and men, plus reserves of up to 150,000; weaponry included 951 main battle tanks. The navy had 7,000 men; vessels included 2 submarines, 3 frigates, 5 corvettes, and 11 OSA missile patrol craft. The air force had 10,000 men, about 242 combat aircraft, and 65 combat helicopters. The gendarmerie totaled 60,000, and the national security forces 20,000. Algeria's defense budget was $1.9 billion in 1998 or about 3.9% of GDP.