Sentence:  Warships, whether surface or submarine, may use <WSD>ruses</WSD> and strategems. They may sail under false flags, both enemy and neutral, but before going into action whether at sea or if about to attack a land target they must strike any false colours and raise their own battle colours. It would be perfidy for them to use the red cross or crescent or any other protected emblem in this way. 
Meaning of the word marked with <WSD> tags:  An action intended to deceive; a trick.