50 USC 2083 - Credit for service while on military leave

(a) General rule 
A participant who, during the period of any war or of any national emergency as proclaimed by the President or declared by the Congress, leaves the participants position in the Agency to enter military service shall not be considered, for purposes of this subchapter, as separated from the participants position in the Agency by reason of such military service, unless the participant applies for and receives a refund of contributions under this subchapter. Such a participant may not be considered as retaining such position in the Agency after December 31, 1956, or upon the expiration of five years of such military service, whichever is later.
(b) Waiver of contributions 
Except to the extent provided under section 2082 (e) or 2082 (h) of this title, contributions shall not be required covering periods of leave of absence from the Agency granted a participant while performing active service in the Armed Forces.