Three navies can be at sea in the same waters doing three different things to the same merchant ship: one escorts it, one boards it, and one turns it back. Each is reported as "naval enforcement", and each rests on a different legal basis and a different kind of evidence. Telling them apart is the first step in reading any claim about what a navy has done to shipping.
Escort: protecting the ship
The simplest activity is protection. Warships accompany merchant vessels through a dangerous stretch of water, shoot down drones and missiles aimed at them, and sometimes put armed teams aboard. The European Union's Operation ASPIDES in the Red Sea is a current example: a mission the EU describes as defensive, whose tasks are maritime situational awareness, accompanying vessels and protecting them against attacks at sea. It has no mandate to search ships or close a coast.
Escort rests on the ordinary right of self-defense and on the consent of the ships being escorted. Its evidence is a count of transits and a record of attacks defeated. A ship that is escorted has not been inspected, and a mission that escorts has not blockaded anyone.
Interdiction: stopping and searching
Maritime interdiction is the broad term for stopping, boarding, searching and, where the law allows, diverting or seizing a vessel. In peacetime the authority has to come from somewhere specific: the consent of the ship's flag state, a treaty such as the drug-trafficking conventions, a UN Security Council resolution enforcing sanctions, or the right to inspect a stateless vessel. Counter-narcotics boardings in the Caribbean and sanctions enforcement against North Korean tankers are interdiction.
In an armed conflict the rules widen. The San Remo Manual on international law applicable to armed conflicts at sea, a 1994 restatement of customary law rather than a treaty, allows a belligerent to visit and search neutral merchant ships, divert them for inspection, and capture those carrying contraband to the enemy. The manual keeps identification, search, diversion and capture as separate steps, and a report should say which one occurred.
The evidence for interdiction is a boarding record: the ship's name and flag, the position and time, the authority invoked, what was found and what happened to the cargo and crew. Position data from AIS transponders can show that a ship changed course, but not why; weather, a charterer's order and a naval instruction all look the same on a track.
Blockade: closing a coast
A blockade is a wartime measure that prevents all ships, friendly or neutral, from entering or leaving enemy ports or a stretch of enemy coast. Under the San Remo Manual's provisions, paragraphs 93 to 104, a blockade must be declared and notified to all states, its start date and geographic limits must be stated, it must be applied impartially to ships of every flag, and it must be effective, meaning actually enforced by a force sufficient to stop traffic. A paper declaration that ships ignore is not a blockade.
The manual also sets limits that protect civilians. A blockade whose sole purpose is to starve the civilian population, or whose expected civilian harm is excessive in relation to the military advantage, is prohibited, and the blockading party must allow passage of essential supplies under conditions it can set. Whether a given blockade meets those conditions is a judgment about a period and a set of actions, not a label that attaches once and stays.
The US naval blockade of Iran, which CENTCOM said on 16 October 2026 has kept $25 billion of Iranian oil off the market, is a current example of a declared blockade enforced over months, running in the same strait where US forces simultaneously escort other countries' ships. The two activities coexist because they have different targets: Iranian cargo on one hand, everyone else's safety on the other.
The Black Sea: attacks are not enforcement
Not every interference with shipping is any of the above. On 6 October 2026 drones hit several commercial vessels in the western Black Sea, including two ships inside Bulgaria's exclusive economic zone for the first time; one, sailing under Togo's flag, sank with its crew reported missing. The day before, a Turkish-owned ship carrying Ukrainian grain sank in Romanian territorial waters after a drone strike that killed two people. Those accounts were given to the UN Security Council on 9 October by the Assistant Secretary-General for political affairs and by several member states, according to the UN's automatic transcript of the meeting.
Russia told the council it does not deliberately target civilian shipping and blamed Ukraine, while citing its own count of attacks on tankers carrying Kazakh oil. Ukraine said Russian attacks had brought traffic through its Black Sea ports to a halt since July. What the council heard were strikes on merchant ships, which the law of naval warfare treats as attacks on civilian vessels rather than as enforcement of a declared and notified blockade. An exclusive economic zone, where some of these strikes occurred, is also not territorial water: coastal states have economic rights there but no sovereignty, which is part of why the incidents alarmed Bulgaria and Romania.
Reading the next naval claim
Three questions sort most reports. What authority did the navy invoke: self-defense, a flag state's consent, a Security Council resolution or the law of blockade? What exactly happened to the ship: accompanied, boarded, diverted, seized or struck? And what record supports the claim: a transit count, a boarding report, a notified blockade declaration, or a video? A naval task group's composition tells you what a navy could do; only the record of individual encounters tells you what it did. The same caution that applies to battlefield claims and combat footage applies at sea, where the vessels involved are usually civilian and the crews rarely get to tell their side.