A Q ship is a regular tramp steamer or merchant cargo ship flying a neutral flag and with false decking and deck houses behind which are mounted 5-inch guns and machine guns. At the sight of the pirates the false sides are droped and the pirates are blasted out of the water.
The Germans used them very effectively during WWII.
Oops, having a little posting trouble this morning?
BTW, I think we got it the first time, but it was the Brits, not the Germans, and it was more effective in WW1 than WW2...