The Soviet Union, believing its only chance of surviving a NATO strike was to preempt it, readied its nuclear arsenal. The CIA reported activity in the Baltic Military District and in Czechoslovakia, and it determined that nuclear-capable aircraft in Poland and East Germany were placed "on high alert status with readying of nuclear strike forces". A 1989 U.S. memorandum said that Soviet commanders ordered nuclear warheads to be placed on 4th Air Army bombers and for Group of Soviet Forces in Germany fighter-bombers to placed on a 30-minute alert. Former CIA analyst Peter Vincent Pry goes further, saying he suspects that the aircraft were merely the tip of the iceberg. He hypothesizes that—in accordance with Soviet military procedure and history—ICBM silos, easily readied and difficult for the United States to detect, were also prepared for a launch.