https://von-hoffmann.livejournal.com/674600.html
In the two world wars, all nations armed their merchant ships with guns and machine guns to protect them from aircraft and submarine attacks. However, an armed merchant ship does not become a warship and therefore does not enjoy the right of hostilities, the right to stop ships at sea, search and seizure. It can use its armament only in self-defence and nothing more.
However, international law does not prohibit the use of military stratagems to mislead the enemy. Examples of such tricks are: the use of camouflage, tactical traps, false operations, means and methods of electronic warfare and disinformation. For example, it was quite possible to draw shadows from gun turrets on the deck of an aircraft carrier in the expectation that not very experienced pilots would mistake it for a battleship, and to put two or three false smoke stacks on one ship to visually transform it into another.
The IX Hague Convention did not resolve the question of where a merchant ship could be turned into a warship, nor did it resolve the question of whether it could be turned back into a merchant ship in time of war. Even then England, the United States, Japan, and Holland defended the position that the conversion of a merchant ship into a warship should only take place in domestic ports and waters. These countries were keen to ensure that ships of other powers with fewer ports than themselves could not fly the military flag on the high seas. Russia, France, Italy and Germany believed that such conversion of merchant ships into military vessels was possible and legal also on the high seas. So the weakest always tried to find a "non-symmetrical answer", but it was not possible to reach an agreement on this issue at that time.
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