Moving prisoners through neutral waters was not automatically unlawful at the time. Once Altmark anchored in internal waters, she had duties to disclose the prisoners and put them ashore, which she did not meet. Britain had compelling moral and military reasons to rescue the sailors. Those reasons did not create a legal right to conduct the boarding in Norwegian waters. Both belligerents therefore violated the law of neutrality, even though Britain's rescue had a strong moral case.
Notable Point · 1:14:58-1:16:32
Why both sides violated neutrality law
Britain's moral and military reasons for rescuing the prisoners did not remove the restrictions imposed by Norwegian neutrality.