10 U.S.C. § 10144

(a) Within the Ready Reserve of each of the reserve components there is an Individual Ready Reserve. The Individual Ready Reserve consists of those members of the Ready Reserve who are not in the Selected Reserve or the inactive National Guard. (b) (1) Within the Individual Ready Reserve of each reserve component there is a category of members, as designated by the Secretary concerned, who are subject to being ordered to active duty involuntarily in accordance with section 12304 of this title . A member may not be placed in that mobilization category unless— (A) the member volunteers for that category; and (B) the member is selected for that category by the Secretary concerned, based upon the needs of the service and the grade and military skills of that member. (2) A member of the Individual Ready Reserve may not be carried in such mobilization category of members after the end of the 24-month period beginning on the date of the separation of the member from active service. (3) The Secretary shall designate the grades and military skills or specialities of members to be eligible for placement in such mobilization category. (4) A member in such mobilization category shall be eligible for benefits (other than pay and training) as are normally available to members of the Selected Reserve, as determined by the Secretary of Defense.