The doctrine of exterritoriality for public ships is a fiction. Public vessels enjoy immunities based on the territorial sovereign's consent, which can be waived. A foreign sovereign's consent to local jurisdiction can be inferred from its conduct, such as permitting its crew to testify in court.

Lord Atkin:-

This is an appeal from the Full Court of Hongkong dismissing an appeal by the appellant from his conviction and sentence at a trial in the Supreme Court of Hongkong before the Chief Justice, MacGregor C. J., and a jury. The appellant was convicted of the murder of Douglas Lorne Campbell and was sentenced to death. The murder was committed on board the Chinese Maritime Customs cruiser "Cheung Keng"while that vessel was in Hongkong territorial waters. Both the murdered man and the appellant were in the service of the Chinese Government as members of the officers and crew of the cruiser. The former was captain: the appellant was cabin boy. Both were British nationals. At the trial, the point was taken that as the murder took place on an armed public vessel of the foreign Government, the British Court had no jurisdiction in the matter. The contention was overruled by the Chief Justice at the trial, and on appeal his decision was upheld by the Full Court over which he presided.

In order to elucidate the legal position it will be necessary to make a short statement of the material facts. On 11th January 1937 the accused shot and killed the captain. He then went up the ladder to the bridge and shot at and wounded the acting chief officer, and then went below and shot and wounded himself. The acting chief officer as soon as he was wounded directed the boatswain to proceed to Hongkong at full speed and hail the police launch. He wanted, he said, help to arrest the accused from the Hongkong police. Within a couple of hours the launch of the Hongkong water police came alongside in answer to the cruiser's signal. The police took the wounded officer and the accused to hospital. They took possession of the two revolvers with which the accused had armed himself, of the spent revolver bullets and expended shells, and of some unexpended cartridges. On 25th February, extradition proceedings were commenced against the accused on the requisition of the chairman of the Provincial Government of Kwangtung alleging murder and attempted murder on board the Chinese Customs cruiser "within the jurisdiction of China while the said cruiser was approximately one mile off Futaumun (British waters)."This appears to be an allegation that the vessel had not at the time reached British territorial waters. The fact that the crime was in reality committed within British waters is not now in dispute. After many adjournments the Magistrate decided, on evidence called for the defence, that the accused was a British national and that the proceedings therefore failed. The accused was at once re-arrested and charged with murder "in the waters of this colony"and duly committed. At the hearing before the Magistrate and at the trial the acting chief officer and three of the crew of the Chinese cruiser were called as witnesses for the prosecution. Police witnesses produced and gave evidence as to the revolvers, cartridge cases and bullets. As has already been stated the accused was convicted and sentenced to death.

On the question of jurisdiction two theories have found favour with persons professing a knowledge of the principles of international law. One is that a public ship of a nation for all purposes either is or is to be treated by other nations as part of the territory of the nation to which she belongs. By this conception will be guided the domestic law of any country in whose territorial waters the ship finds herself. There will therefore be no jurisdiction in fact in any Court where jurisdiction depends upon the act in question or the party to the proceedings being done or found or resident in the local territory. The other theory is that a public ship in foreign waters is not and is not treated as territory of her own nation. The domestic Courts in accordance with principles of international law will accord to the ship and its crew and its contents certain immunities, some of which are well settled, though others are in dispute. In this view the immuni