5 CFR §875.204

1. (a)You are eligible to apply for coverage if you are on active duty or full-time National Guard duty for more than a 30-day period.
2. (b)You are eligible to apply for coverage if you are a member of the Selected Reserve, which consists of:
   1. (1)Drilling Reservists and Guardsmembers assigned to Reserve Component Units;
   2. (2)Individual Mobilization Augmentees who are Reservists assigned to Reserve Component billets in Active Component units (you may be performing duty in a pay or non-pay status); and
   3. (3)Active Guard and Reserve members who are full-time Reserve members on full-time National Guard duty or active duty in support of the National Guard or Reserves.
3. (c)You are not eligible to apply for coverage solely because you belong to the Individual Ready Reserve. The Individual Ready Reserves includes Reservists who are assigned to a Voluntary Training Unit in the Naval Reserve and Category E in the Air Force Reserve.