; selective early retirement (a) Retirement for years of services Sections 633 through 636 of this title shall apply to the retirement of officers in competitive categories of officers designated for purposes of this subchapter. (b) Selective early retirement Sections 638 and 638a of this title shall apply to the retirement of officers described in subsection (a). 649h. Continuation on active duty (a) In general An officer subject to discharge or retirement pursuant to this subchapter may, subject to the needs of the service, be continued on active duty if the officer is selected for continuation on active duty in accordance with this section by a selection board convened under section 611(b) of this title. (b) Identification of positions for officers continued on active duty (1) In general Officers may be selected for continuation on active duty pursuant to this section only for assignment to positions identified by the Secretary of the military department concerned for which vacancies exist or are anticipated to exist. (2) Identification Before convening a selection board pursuant to section 611(b) of this title for purposes of selection of officers for continuation on active duty pursuant to this section, the Secretary of the military department concerned shall specify for purposes of the board the positions identified by the Secretary to which officers selected for continuation on active duty may be assigned. (c) Recommendation for continuation A selection board may recommend an officer for continuation on active duty pursuant to this section only if the board determines that the officer is qualified for assignment to one or more positions identified pursuant to subsection (b) on the basis of skills, knowledge, and behavior required of an officer to perform successfully in such position or positions. (d) Approval of Secretary of military department Continuation of an officer on active duty under this section pursuant to the action of a selection board is subject to the approval of the Secretary of the