Unrestricted Warfare was first introduced in the first world war by the German navy. The strategy was to sink vessels without warning, the most famous incident being the sinking of the RMS "Lusitania". The strategy was considered controversial and many navies (the U. S. especially) asked Germany to stop using said strategy. Germany stopped for a bit but resumed using the strategy to attack British freighters that carried food so they could starve the British. After the resuming of the strategy, many countries tried to limit the use of submarines altogether. The strategy was never abolished; rather, other navies started using it.