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How do marine blockades work?

Neil Roberts
Head of Marine and Aviation

Blockades can occur in peacetime but are more usual in war. Legally, war is a state of affairs, not an event or an occurrence, so for example, WW2 was not an event for insurance purposes.
A blockade is a restraint (covered by war insurers under CL281) carried out by a sovereign power utilising military force. This is no different in principle to a land siege and similar in effect to an embargo, although the scale of intent will vary and it is possible to embargo goods without military force e.g. the French restrictions on British beef. Embargos are financial or legal rather than physical.

Like sanctions, the effects of blockades are variable and not immediately conclusive. Sanctions seek to impair financial ability and weaken an economy; military blockades seek to paralyse a state or port by physically restricting or sealing off access. Their objective is to weaken an enemy’s ability to pursue military action by reducing or cutting the supply of military and civilian goods. They are designed to force the opponent to negotiate terms for surrender, but they can and do cause starvation of the target country’s population as in Germany 1918 , and Iraq after 2003.

Belligerent nations have the right to stop and search neutral vessels at sea under international law but the definition of contraband was historically grey and had similarities to the issues around dual-use goods now. A complication is the right of angary which involves paying compensation for seized goods. A variant, the limited blockade, can also be used, to target certain defined goods in a contested area.
Pacific blockades are coercive measures used in peacetime to achieve ends but without kinetic military action; they have no agreed legal status so parameters are virtually limitless. At sea, they rely on the use of naval power to enforce these but not to engage militarily. For the sake of international relations, they cannot be used against neutrals.

Such pacific blockades were usually carried out by a more powerful nation/coalition up to 1914 against a weaker opponent and ended when it was thought that the aim was achieved, or the situation had evolved to a point where conflict was not needed. A pacific blockade is not war, and neither are the more regulated sanctions that effectively supplanted them. A pacific blockade could be used to help enforce sanctions although it would require extensive naval support.
Interestingly, not all blockades are imposed for political, military or economic reasons. It is worth remembering that Britain mounted a blockade of the African coast to halt the transatlantic slave trade.

This piece was originally posted on LinkedIn and you can access this here.

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