Final answer:
Sailors may need medical waivers for conditions that normally disqualify them from service. Medical deferments were historically used as a draft avoidance strategy. Standards for waivers varied by local draft boards, and waivers could be crucial during hazardous sailing periods, such as in the military or on slave ships.
Step-by-step explanation:
A sailor might require medical waiver due to physical or mental health conditions that would typically disqualify them from service. During periods such as the Vietnam War, some individuals sought medical deferments as a means to avoid the draft, and local draft boards determined the eligibility and qualifications, leading to a variety of standards. Furthermore, as historical contexts like World War II illustrate, sailors like any military personnel, may require medical waivers if they have conditions that do not actually prevent them from performing their duties.
The necessity for medical waivers can also arise from historical practices such as the use of blue discharges to expel gay servicemen or the high risks associated with the spread of diseases like trachoma on slave ships, which could lead to blindness and the need for medical waivers for affected sailors.