Final answer:
Retired sailors retained on active duty must make an SBP election upon reaching retirement eligibility or at retirement, as it is crucial for the financial security of their dependents.
Step-by-step explanation:
Sailors who are retained on active duty are expected to make a valid Survivor Benefit Plan (SBP) election when they reach retirement eligibility or upon actual retirement. The SBP allows retired service members to ensure that their family members continue to receive a portion of their retirement benefits after their death. Making a timely and informed election is crucial, as it affects the financial security of a sailor's dependents. It is a significant transition point requiring socialization into a new role, much like turning eighteen requires U.S. males to register with the Selective Service System.