of intervention if a country appeared to be violating core socialist ideas, explicitly stated in the Brezhnev Doctrine. Notable military exercises "Szczecin" (Poland, 1962) "Vltava" (Czechoslovakia, 1966) Operation "Rhodope" (Bulgaria, 1967) "Oder-Neisse" (East Germany, 1969) Przyjaźń 84 (Poland, 1984) Shield 84 (Czechoslovakia, 1984) NATO and Warsaw Pact: comparison of the two forces NATO and Warsaw Pact forces in Europe {| class="wikitable" |+ Data published by the two alliances (1988–1989) |- ! | colspan="2" |NATO estimates | colspan="2" |Warsaw Pact estimates|- | Type || NATO || Warsaw Pact || NATO || Warsaw Pact'|- | Personnel || 2,213,593 || 3,090,000 || 3,660,200 || 3,573,100 |- | Combat aircraft || 3,977 || 8,250 || 7,130 || 7,876 |- | Total strike aircraft || NA || NA || 4,075 || 2,783 |- | Helicopters || 2,419 || 3,700 || 5,720 || 2,785 |- | Tactical missile launchers || NA || NA || 136 || 1,608 |- | Tanks || 16,424 || 51,500 || 30,690 || 59,470 |- | Anti-tank weapons || 18,240 || 44,200 || 18,070 || 11,465 |- | Armored infantry fighting vehicles || 4,153 || 22,400 || 46,900 || 70,330 |- | Artillery || 14,458 || 43,400 || 57,060 || 71,560 |- | Other armored vehicles || 35,351 || 71,000 || || |- | Armored vehicle launch bridges || 454 || 2,550 || || |- | Air defense systems || 10,309 || 24,400 || || |- | Submarines || || || 200 || 228 |- | Submarines (nuclear powered) || || || 76 || 80 |- | Large surface ships || || || 499 || 102 |- | Aircraft-carrying ships || || || 15 || 2 |- | Aircraft-carrying ships armed with cruise missiles || || || 274 || 23 |- | Amphibious warfare ships || || || 84 || 24 |} Post–Warsaw Pact On 12 March 1999, the Czech Republic, Hungary, and Poland joined NATO; Bulgaria, Estonia, Latvia, Lithuania, Romania, and Slovakia joined in March 2004; Albania joined on 1 April 2009. Russia and some other post-USSR states joined the Collective Security Treaty Organization (CSTO) in 1992, or the Shanghai Five in 1996, which was renamed the Shanghai Cooperation Organisation (SCO) after Uzbekistan's addition in 2001. In November 2005, the Polish government opened its Warsaw Treaty archives to the Institute of National Remembrance, which published some 1,300 declassified documents in January 2006, yet the Polish government reserved publication of 100 documents,