The MR 31 was a French nuclear warhead for the S2 medium-range ballistic missile. The weapon had a yield of 120 kilotonnes of TNT (0.50 PJ) and weighed 700 kilograms (1,500 lb). It was apparently a pure plutonium device and unboosted, and the largest pure plutonium weapon ever built. Entering service in August 1970 it was withdrawn from service by June 1980.
== See also == force de frappe FOST nuclear tests by France