((a)) The Secretary may provide a bonus, not to exceed $20,000, to an enlisted member who completes training in a skill designated as critical, if at least four years of obligated active service remain on the member’s enlistment at the time the training is completed. A bonus under this section may be paid in a single lump sum or in periodic installments.

((b)) If an enlisted member voluntarily or because of misconduct does not complete the member’s term of obligated active service, the Secretary may require the member to repay the United States, on a pro rata basis, all sums paid under this section. The Secretary may charge interest on the amount repaid at a rate, to be determined quarterly, equal to 150 percent of the average of the yields on the 91-day Treasury bills auctioned during the calendar quarter preceding the date on which the amount to be repaid is determined.