Neutrality theoretically permits commerce with both sides, but a blockade gives the enforcing power strong reasons to limit that trade. Napoleon's sweeping demands are contrasted with Britain's decision not to rescue the Confederacy by openly trading through the Union blockade. The world wars made identification even more dangerous because submarines had limited time and range in which to establish a ship's flag or passenger status. The Asama Maru and SS Vincent de Paul incidents illustrate how supposedly neutral shipping could carry enemy personnel or operate through disputed waters. Neutral rights become a diplomatic and operational problem as soon as a navy tries to police maritime traffic.
Chapter · 27:45-30:48
Neutral rights, contraband, and maritime coercion
Blockade enforcement creates immediate disputes over neutral shipping, from whether neutrals may trade with both belligerents to whether a submarine can identify a ship before attacking it.