No, that’s not the sound of a musket shot. It’s an emergency message.
When a vessel sends the “PAN PAN, PAN PAN, PAN PAN” signal (and it actually has to be repeated three times) it means that there is a serious problem on board. This could involve someone who has been injured or fallen ill, an engine problem that prevents the ship from returning to port on its own, or any other major breakdown.
The captain who sends this message follows the code with the vessel’s name, the nature of the emergency, the assistance requested, the number of people on board and any other information that might prove useful.
In the hierarchy of emergencies, a “PAN PAN, PAN PAN, PAN PAN” message is treated like the well-known distress call “MAYDAY, MAYDAY, MAYDAY.” The latter is reserved for extreme situations that endanger human life, for example a sinking ship or a fire on board. The “MAYDAY” message takes the highest priority.
Here’s a trick to keep the two signals straight:
MAYDAY is pronounced “m’aider” in French, or “help me,” and means we need help immediately, that it’s a matter of life and death.
PAN PAN is pronounced “panne panne” in French, or “breakdown,” and means that something has broken down, that the vessel needs help, but no person is at any risk of death.