I do not think all merchant ships could be armed as you like for defence. There is a limit , so then the ship will be regarded as a wrship.
These ships listed by lete Colledge & Dittmar are Q-ships, ie de facto warshisps.
Basic data regarding WWI are below.
Hague VII: Conversion of Merchant Ships into War Ships.
Please note that privateering was abolished after the Congress of Paris of 1856 at the end of Crimean War.
Perhaps sombody better know in the international maritime law, could simply presented which ship should be considered as a merchant vessel, when they are piracy ships, etc.
Edited 1 time(s). Last edit at 01/20/2018 12:59PM by Andreas von Mach.