This article examines when states are allowed to use force against neutral merchant ships outside territorial waters. This is regulated by both international humanitarian law and the prohibition of the use of force, which apply concurrently to naval warfare. The prohibition of the use of force imposes narrower limits than international humanitarian law, in the sense that certain actions that have traditionally been permitted under international humanitarian law are contrary to the prohibition of the use of force. The prohibition of the use of force exempts uses of force based on UN Security Council resolutions, consent and self-defence. Where there is no UN Security Council resolution or consent, self-defence remains the only option, and self-defence does not give a right to direct the use of force towards third states or their ships. Therefore, the right to self-defence does not permit blockades outside territorial waters or visit and search operations that are not founded on specific suspicions against individual ships, even though such operations may be permitted under international humanitarian law. These conclusions are supported by an examination of state practice and opinio juris, where the few relevant instances that do exist have met with widespread protests from other states.

Incidents at sea between warships and military aircraft often involve more than provocative actions – they may be aggressive and can sometimes result in death and destruction. In view of the low threshold of a resort to armed force by one State against another that would bring an international armed conflict into existence, it is rather difficult to determine whether incidents at sea remain below that threshold. Similar, albeit less difficult problems arise with regard to forceful measures taken by States against foreign merchant vessels. Here it is important to clearly distinguish between law enforcement at sea and the exercise of belligerent rights.

Visit and Search — Spoliation of Ship’s Papers — Attempt to Scuttle Ship — Whether a Reason for Condemnation.

Visit and Search — Detention — Whether Deemed to Have Taken Place on the High Seas or in Port — Article 297 (e) of the Treaty of Versailles.

Jurisdiction — In General — Locality of — Detention of Neutral Ships as the Result of Stoppage on the High Seas — Whether Deemed to Have Taken Place on the High Seas — Article 297 (e) of the Treaty of Versailles.