A participant who is entitled to an immediate annuity under subsection (b) of this section shall be entitled to receive an annuity supplement while the annuitant is under 62 years of age. The annuity supplement shall be based on the total creditable service of the annuitant and shall be computed in accordance with sections
8421
(b) and
8421a of title
5 as if the participant were a law enforcement officer retired under section 8412(d) of such title.