What must active duty family members sign up for before their sponsor's retirement date to avoid a gap in TRICARE coverage?

Active duty family members must sign up for Medicare Part B before their sponsor's retirement date to avoid a gap in TRICARE coverage. When a service member retires, their family members may lose eligibility for certain types of TRICARE coverage unless they transition to Medicare. Medicare Part B is essential as it provides coverage for outpatient services that TRICARE does not cover entirely, especially after transitioning from active duty status. Ensuring enrollment in Medicare Part B allows beneficiaries to have continuous health coverage without interruptions, which is crucial for maintaining their overall health care management during the transition from TRICARE's active duty benefits to those available for retired personnel and their families.