Which of the following situations leads to a change in TRICARE eligibility?

Retirement from active duty is a significant life event that directly impacts TRICARE eligibility. When a service member retires, they transition from active duty status, which qualifies them for TRICARE coverage, to a retired status, which can come with different rules and plans under TRICARE, such as TRICARE Prime, TRICARE Select, or other options available for retirees and their families. This change emphasizes the importance of understanding how changes in military status affect health care benefits.

In contrast, other situations such as moving to a new address or completing a training program do not inherently alter TRICARE eligibility. While these events may require updating personal information or could impact the type of plan selected (like affecting regional coverage for services), they do not fundamentally change a person's eligibility status for TRICARE benefits. Changing branches of service may involve transfer processes but does not automatically change eligibility status either, as military members continue to qualify for TRICARE as long as they are on active duty or reserves. Thus, retirement from active duty clearly stands out as the situation that leads to a change in TRICARE eligibility.