5 USC 3341 - Details; within Executive or military departments

(a) The head of an Executive department or military department may detail employees among the bureaus and offices of his department, except employees who are required by law to be exclusively engaged on some specific work.
(1) Details under subsection (a) of this section may be made only by written order of the head of the department, and may be for not more than 120 days. These details may be renewed by written order of the head of the department, in each particular case, for periods not exceeding 120 days.
(2) The 120-day limitation in paragraph (1) for details and renewals of details does not apply to the Department of Defense in the case of a detail

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(A) made in connection with the closure or realignment of a military installation pursuant to a base closure law or an organizational restructuring of the Department as part of a reduction in the size of the armed forces or the civilian workforce of the Department; and
(B) in which the position to which the employee is detailed is eliminated on or before the date of the closure, realignment, or restructuring.
(c) For purposes of this section, the term base closure law has the meaning given such term in section 101 (a)(17) of title 10.