172 1. The Biological and Toxin Weapons Con ven tion (BTWC) was opened for signature on 10 April 1972 and entered into force on 26 March 1975. The Co-Depositaries for this Convention are the Russian Federation, the United King dom and the United States. This Convention was the first one to totally prohibit the development, production and stockpiling of a class of weapons of mass destruction — that involving the use of biological agents and toxins as weapons. The Ukraine was one of the original States Parties who signed the Convention on 10 April 1972 and for whom the Convention entered into force on 26 March 1975. The central prohibition is set out in Article I of the Convention [1] under which: Each State Party to this Convention undertakes never in any circumstances to develop, produce, stockpile or otherwise acquire or retain: (1) Microbial or other biological agents, or toxins whatever their origin or method of production, of types and quantities that have no justification for prophylactic, protective or other peaceful purposes; (2) Weapons, equipment or means of delivery designed to use such agents or toxins for hostile purposes or in armed conflict. 2. In accordance with Article XII of the Convention, Review Conferences have been held at five year intervals — in 1981, 1986, 1991, 1996, 2001/2, 2006 and 2011 — to UDK 608.3+623.458