What must SEALs wear while operating the SDV due to its design?

The correct choice is to wear an Underwater Breathing Apparatus while operating the SDV (Swimmer Delivery Vehicle). This is essential because the SDV is designed for operations that take place underwater, often at considerable depths. The Underwater Breathing Apparatus allows SEALs to breathe while submerged, ensuring they can operate effectively and safely during missions.

The apparatus typically includes components such as tanks for storing breathing gas, regulators to provide a breathable atmosphere, and sometimes specialized accessories for communication and navigation. Using this equipment allows SEALs to maintain necessary oxygen levels and stay submerged for extended periods, which is crucial in the context of covert operations and infiltration.

If SEALs were to opt for other clothing or equipment options, they would be compromising their ability to effectively engage in underwater operations, which can include everything from reconnaissance to the delivery and recovery of personnel or equipment. Thus, the Underwater Breathing Apparatus is not only practical but vital for their success and safety during such missions.