During the last half of FY 1961, OCDM began a series of quarterly operational exercises (OPEX-Series) principally to check emergency operational procedures and facilities more frequently and to test and exercise key emergency personnel in government more frequently and intensively. OPEX 1961-I, held on January 16, briefly covered the readiness preattack phase and the early stages of a nuclear attack phase. Only selected OCDM staff participated. OPEX 1961-II, held on April 6 and 7, was similar but included Federal agency headquarters and field staffs whose emergency plans require presence at OCDM facilities. (OCDM, Annual Report 1961, p. 88)