(a) A member of the Fleet Reserve or the Fleet Marine Corps Reserve may be ordered by competent authority to active duty without his consent—

(1) in time of war or national emergency declared by Congress, for the duration of the war or national emergency and for six months thereafter;

(2) in time of national emergency declared by the President; or

(3) when otherwise authorized by law.

(b) In time of peace any member of the Fleet Reserve or the Fleet Marine Corps Reserve may be required to perform not more than two months’ active duty for training in each four-year period.