A distress call from a ship far from any coast reaches help through a system that barely cares where the vessel is registered. The ocean is divided into rescue regions, each with a country on duty.
The ocean is carved into rescue regions
Coastal states agree among themselves which stretch of sea each will take responsibility for, and between them those regions cover the whole ocean surface.
A region can extend far beyond a country's territorial waters or its economic zone. Rescue duty is kept deliberately separate from any claim over the sea itself.
That separation removes the argument. A ship in trouble need not establish whose water it sits in before anybody starts moving toward it.
A coordination center runs the case
Each region is run from a center staffed around the clock, which takes the alert, fixes a position and works out what can reach the scene soonest. In American waters that role sits with the Coast Guard.
The center rarely owns the assets it sends. It directs cutters, aircraft and, more often than anything else, merchant ships that happen to be nearby.
Coordination is the scarce skill, not the hardware. Turning a drifting position and a wind estimate into a search area decides whether anything is found.
Passing merchant ships carry the legal duty
Masters of vessels at sea must assist people in distress when they can do so without serious danger to their own ship and crew. The obligation attaches to the ship, not to its owner's nationality.
So a loaded container ship on a schedule can be turned around by a call it never expected, and it goes. The diversion may cost it a berth slot at the far end.
Fuel and delay fall on the operator. The duty is written without a commercial exemption, because a rescue that waits for a cost discussion is not a rescue.
Alerts arrive on several independent channels
Distress signals travel by satellite beacon, by digital radio call and by voice, because any single channel can fail at the moment it is needed.
A beacon transmits an identity that traces back to a registered vessel or aircraft. That lets a center confirm who is missing instead of searching on an anonymous signal.
Duplicate alerts for one incident are normal and get merged into a single case. Centers work at that so two half-strength searches do not run in parallel.
Landing the survivors is a separate problem
Pulling people out of the water ends the emergency but not the case, because somebody has to accept them ashore and that requires a port state to agree.
Disembarkation is negotiated rather than automatic. It can turn on immigration status, on medical need, and on where the rescuing ship was going before it was diverted.
The friction sits here rather than in the search, which is why a center starts working on a landing place while the ship is still on scene.