|Click any image to enlarge|
German U-boat captains had to calculate a boat's course and speed to properly lead their torpedo shots to hit the target. Dazzle patterns made it difficult for a captain to accurately judge the heading of his target's bow. In addition, U-boaters refined their calculation of a ship's course and speed by aligning two mirrors inside of the periscope, and dazzle patterns made that difficult to do.
The effectiveness of dazzle painting is in dispute. Regardless, with the advent of radar and more sophisticated optics, the patterns fell into disuse. Besides, the Admirals never liked seeing their boats painted so garishly to begin with.
It is a shame all we have are black and white pictures of the boats because, as you can see in the sample below, they were often painted in very bright colors as well as bold patterns. There are more examples of ship's wearing dazzle patterns after the jump.