Lt. Col. (res.) Maurice Hirsch
Jerusalem Center for Security and Foreign Affairs, June 4, 2025
“To destroy Hamas’s military capabilities and dismantle its governance capabilities, Israel needs to ensure, among other things, that it prevents Hamas from rearming and from receiving funds that it critically needs to support both its terrorist activities and its governance mechanisms.”
According to the Laws of War and the Laws of the Sea, any vessel that attempts to breach a legally imposed maritime blockade becomes a legitimate military target. The country that imposed the blockade is thus entitled, and possibly even required, to use all necessary force to prevent the intended breach. So, when Greta Thunberg and “Game of Thrones” actor Liam Cunningham decided to board the latest terrorist-propaganda mission aboard the Madleen with the stated goal of breaking the maritime blockade imposed by Israel on Gaza, they and their fellows were knowingly taking their lives in their hands, and bear the sole responsibility for any outcome.
What Rules Guide Maritime Blockades?
Maritime blockades have been in existence for hundreds of years.1 In modern warfare, maritime blockades were explicitly mentioned in the 1856 Declaration of Paris Respecting Maritime Law,2 with more detailed requirements set out in the 1909 London Declaration on Naval Warfare.3 Most recently, the subject of maritime blockades was also extensively addressed in the 1994 San Remo Manual on International Law Applicable to Armed Conflicts at Sea.4
According to these rules, a blockade is legal if it meets certain cumulative requirements:
- A blockade shall be declared and notified to all belligerents and neutral States.5
- The declaration shall specify the commencement, duration, location, and extent of the blockade and the period within which vessels of neutral States may leave the blockaded coastline.6
- A blockade must be effective7 – i.e., maintained by forces that are sufficient to render ingress or egress of the blockaded area dangerous.
- A blockade must not bar access to the ports and coasts of neutral States.8
- A blockade must be applied impartially to the vessels of all States.9
If a blockade conforms with the above requirements, the party that implemented the blockade may, if it has reasonable grounds to believe that a merchant vessel10 intends to breach the blockade, act to capture the vessel or even, if the vessel refuses to heed the warning and desist from an attempt to breach the blockade, attack the vessel.11
To act against a vessel that has the clear intention of breaching a blockade, the party that implemented the blockade does not have to wait until the blockade is actually breached.12 ….SOURCE