Turns out, dazzle camouflage wasn’t the main reason enemy subs were misled in World War I, it was a natural visual illusion called the “horizon effect.” Aston University scientists revisited a century-old experiment and uncovered that perception, not paint, played the biggest role in the confusion.
- During World War I, ships were painted with geometric “dazzle” camouflage to confuse enemy observers about their speed and direction.
- Researchers Timothy Meese and Samantha Strong reanalyzed a 1919 dataset and found that a visual illusion called the “horizon effect” was actually more effective at creating confusion.
- The horizon effect occurs when a distant ship appears to move along the horizon line, even if it’s traveling at an angle, causing observers to misjudge its true course.
Reexamining Dazzle Camouflage with Modern Tools
A new analysis by Aston University researchers, Professor Tim Meese and Dr. Samantha Strong, has revisited 105-year-old data on the effectiveness of “dazzle” camouflage used on battleships during World War I. Their findings show that while dazzle camouflage had some impact, a different visual illusion, known as the “horizon effect,” played a much larger role in confusing enemy observers.
In World War I, navies painted ships with bold, geometric patterns called dazzle camouflage. The goal was to mislead enemy U-boat captains about a ship’s speed and direction, making it more difficult to launch accurate torpedo attacks.
The Overlooked Horizon Illusion
However, the researchers highlight the powerful influence of the “horizon effect.” This illusion occurs when a distant ship appears to move along the horizon line, regardless of its actual course. Ships traveling at angles up to 25 degrees from the horizon often appear to be moving straight along it, and even at larger angles, observers tend to underestimate the deviation.
Despite widespread use of dazzle camouflage, it was not until 1919 that a proper, quantitative study was carried out, by MIT naval architecture and marine engineering student Leo Blodgett for his degree thesis. He painted model ships in dazzle patterns and placed them in a mechanical test theatre with a periscope, like those used by U-boat captains, to measure how much onlookers’ estimations of the ships’ direction of travel deviated from their actual direction of travel.
Revisiting Blodgett’s Data with Fresh Eyes
Professor Meese and Dr. Strong realized that while the data collected by Blodgett was useful, his methods of experimental design fell short of modern standards. He’d found that dazzle camouflage worked, but the Aston University team suspected that dazzle alone was not responsible for the results seen, cleaned the data and designed new analysis to better understand what it really shows.
Dr. Strong, a senior lecturer at Aston University’s School of Optometry, said:
“It’s necessary to have a control condition to draw firm conclusions, and Blodgett’s report of his own control was too vague to be useful. We ran our own version of the experiment using photographs from his thesis and compared the results across the original dazzle camouflage versions and versions with the camouflage edited out. Our experiment worked well. Both types of ships produced the horizon effect, but the dazzle imposed an additional twist.”
Reconstructing the Experiment with a Control
If the errors made by the onlookers in the perceived direction of travel of the ship were entirely due to the ‘twist’ on perspective caused by dazzle paintwork, the bow, or front, of the ship, would always be seen to twist away from its true direction. However, Professor Meese and Dr. Strong instead showed that when the true direction was pointing away from the observer, the bow was often perceived to twist towards the observer instead. Their detailed analysis showed a small effect of twist from the dazzle camouflage but a much larger one from the horizon effect. Sometimes these effects were in competition, sometimes in harmony.
Expertise Doesn’t Override Visual Bias
Professor Meese, a professor of vision science at the School of Optometry, said:
“We knew already about the twist and horizon effects from contemporary computer-based work with colleagues at Abertay University. The remarkable finding here is that these same two effects, in similar proportions, are clearly evident in participants familiar with the art of camouflage deception, including a lieutenant in a European navy. This adds considerable credibility to our earlier conclusions by showing that the horizon effect, which has nothing to do with dazzle, was not overcome by those best placed to know better.
The Horizon Effect’s Lasting Deceptive Power
“This is a clear case where visual perception is more powerful than knowledge. In fact, back in the dazzle days, the horizon effect was not identified at all, and Blodgett’s measurements of perceptual bias were attributed entirely to the camouflage, deceiving the deceivers.”
Professor Meese and Dr. Strong say that more work is required to fully understand how dazzle might have increased perceptual uncertainty of direction and speed but also the geometry behind torpedo-aiming tactics that might have supported some countermeasures.
Reference: “Blodgett’s (1919) “Ship camouflage” 105 years on: A misperception of dazzle perception revealed and redressed” by Timothy Simon Meese and Samantha Louise Strong, 1 March 2025, i-Perception.
DOI: 10.1177/20416695241312316
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