Summary from the GAO website:
The Servicemembers Civil Relief Act (SCRA) provides servicemembers with an interest rate cap of 6 percent on student loans while they are on active duty. The number of servicemembers with federal student loans who received this rate cap increased as a result of the Department of Education (Education) requiring federal loan servicers to regularly use the Department of Defense’s (DOD) SCRA website to identify eligible servicemembers and automatically apply the rate cap without requiring servicemembers to provide written notice of active duty (see figure). Using the automated process, some federal loan servicers identified borrowers who had been eligible for the rate cap as far back as 2008, when the SCRA rate cap first applied to federal loans, and retroactively applied the cap.