As noted in the
Medicare & You Handbook:
If you have Medicare Part A (hospital and in-patient coverage) and TRICARE (insurance for active-duty military, military retirees, and their families), you must also have Medicare Part B (doctor visit and out-patient coverage) to keep your TRICARE coverage.
However, if you’re an active-duty service member, or the spouse or dependent child of an active-duty service member:
- You don’t have to enroll in Medicare Part B to keep your TRICARE coverage while the service member is on active duty.
- Before the active-duty service member retires, you must enroll in Medicare Part B to keep TRICARE without a break in coverage.
- You can get Medicare Part B during a Special Enrollment Period (SEP) if you have Medicare because you’re 65 or older, or you’re disabled.
- You should enroll in Medicare Part A and Medicare Part B when you’re first eligible based on ESRD (End Stage Renal Disease)