Jun 112011
 
Dazzle-ships in Drydock at Liverpool

Image via Wikipedia

IN THE second world war, many Allied ships were painted with dark and light stripes, and other contrasting shapes, making them look a bit like zebra. The idea was to distort an enemy submarine commander’s perception of the ship’s size, shape, range, heading and speed, so as to make it harder to hit with the non-homing torpedoes of the period. These had to be pointed not at the target directly but, rather, at the place where the commander thought the target would be when the torpedo arrived. At the time, it was only an educated guess that this so-called dazzle camouflage would work. But now someone has actually tested it and the short answer is that it does work—but not in the way that Allied navies thought it did. Ships move too slowly. Dazzle camouflage might well, however, have a role in protecting faster-moving vehicles, such as military Land Rovers.

Nicholas Scott-Samuel, of the University of Bristol, and his colleagues came to this conclusion by asking volunteers to watch patterned rectangles cross a computer screen. Some of the rectangles had horizontal stripes inside them. Some had vertical stripes. Some had zig-zags. And some had checks. Some, acting as controls, had no internal patterns. Each test involved a jazzy rectangle crossing the screen either before or after a plain one. Volunteers had to estimate which of the two was travelling faster.

In fact, in all cases, the two rectangles travelled at the same speed. But the researchers varied the conditions in other ways, without telling the participants. Sometimes both rectangles travelled slowly, at just over 3º of arc a second from the observer’s point of view, mimicking a ship. Sometimes they travelled much faster, at 20º a second, mimicking a land vehicle. The jazzy rectangles also differed. Some were low contrast (ie, not very jazzy) and some high contrast.

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