I presume by pointing a lot of guns at them and threaten to blow them up or demand permission to board, as per the rules of war at the time. Submarines didn't really have that option.
I would also note that the Lusitania was not a neutral ship. It was British flagged. A big issue was that the submarines would fire on commercial vessels without warning.
The US government didn't really have the authority to tell civilians they couldn't board a single vessel.
As for the sinking, the rules of war (that were outdates and did not consider the nature of submarine warfare) allowed for the sinking of the Lusitania, or any commercial vessel, but required that all crew and passengers be removed to a safe location first, unless the captain refused to allow the raiders to board.
As for supplying arms to the British, they also supplied the Germans, but it was difficult for the Germans to get anything from the US to Europe.
I would also note that the Lusitania was not a neutral ship. It was British flagged. A big issue was that the submarines would fire on commercial vessels without warning.
Are you suggesting that the sinking of the Lusitania was a deliberate plot by the US government to get into a war with Germany?it was obviously known that the US was supplying arms and ammunition to the Brits, hence a
valid target.
Yet, as is with US, they chose to sacrifice the some 1000 people so that the country would be ready for another war ...
The US government didn't really have the authority to tell civilians they couldn't board a single vessel.
As for the sinking, the rules of war (that were outdates and did not consider the nature of submarine warfare) allowed for the sinking of the Lusitania, or any commercial vessel, but required that all crew and passengers be removed to a safe location first, unless the captain refused to allow the raiders to board.
As for supplying arms to the British, they also supplied the Germans, but it was difficult for the Germans to get anything from the US to Europe.