In which situation should a vessel use visual distress signals?

A vessel should use visual distress signals primarily when in need of rescue. Visual distress signals are intended to convey emergencies to other vessels or nearby land, indicating that the vessel requires assistance. This includes situations such as capsizing, running aground, or any condition that places the vessel and its crew in imminent danger.

While it may be tempting to think about using distress signals in other contexts, such as close proximity to other vessels or during reduced visibility, these situations do not inherently require the use of distress signals. Visual signals are specifically designed to alert others to dire circumstances. Therefore, the use of these signals should be reserved for situations where there is a clear need for rescue, making option C the most appropriate choice.