Each member of the armed forces who accepts a fellowship, scholarship, or grant in accordance with subsection (a) shall, before he is permitted to undertake the education or training contemplated by that fellowship, scholarship, or grant, agree in writing that, after he completes the education or training, he will serve on active duty for a period determined by the Secretary concerned, which may not be less than twice the length of the period of the education or training. Notwithstanding
section 2004(c) of this title, the service obligation required under this subsection may run concurrently with any service obligations incurred under chapter 101 of this title in accordance with regulations established by the Secretary concerned.