During what condition is the ship required to sound the man overboard alarm?

The correct answer is rooted in the primary objective of ensuring the safety of personnel on board. The man overboard alarm is specifically designed to alert the crew and mobilize an immediate response when someone falls overboard. This action is critical because the faster the crew can react, the higher the chances are of recovering the individual safely. Promptly sounding the alarm initiates search and rescue procedures, which can include deploying rescue boats and designating lookout positions.

Other choices do not align with the protocol for responding to a man overboard situation. Sounding the alarm every time the ship departs would not be practical, as it could desensitize the crew to the alarm's urgency. Additionally, using the alarm only during drills would not serve its critical purpose of a real-time response in an emergency. Lastly, sounding the alarm upon entering port does not pertain to the man overboard protocol and is unrelated to immediate life-saving responses required if someone falls into the water. Thus, the requirement to sound the man overboard alarm is specifically enacted when a person actually falls overboard.