What required safety equipment must be on board when operating a vessel?

The correct choice emphasizes the importance of having essential safety equipment on board a vessel to ensure the safety of those on board and to enable effective communication and emergency responses.

A functioning marine radio is crucial as it allows for communication with other vessels and shore stations, which can be vital in emergencies. Life jackets are fundamental safety items that should be provided for every person on the vessel; they significantly increase the chances of survival in the event of an accident. Distress signals, which can include flares or electronic signaling devices, are essential for alerting others when a vessel is in distress and requires assistance.

The other choices, while they may contain useful equipment, do not encompass the critical combination of tools needed for emergency situations and overall safety while operating a vessel. For instance, a fire extinguisher and first aid kit are important, but they do not address communication and distress signaling capabilities, which are vital for safety at sea. Extra fuel and a replacement engine are more about operational continuity rather than immediate safety concerns. Similarly, a compass and depth sounder aid navigation but do not provide direct assistance in distress situations.