Similarly in America, while "the draft" ended in 1973, laws require men to register with the SelectiveServiceSystem within 30 days of their 18th birthday.
However, the SelectiveServiceSystem remains in place as a contingency plan; men between the ages of 18 and 25 are required to register so that a draft can be readily resumed if needed.
On March 21, 1970, I got a letter from Lee Williams saying that he had talked to Colonel Lefty Hawkins, the head of the Arkansas SelectiveServiceSystem, who told him we would all be called.