Haven’t done one of these in a while, but I went down a rathole doing some research, so you get a post with pictures… LOL
Determining the range, size, heading, and speed of a ship at sea, before radar was invented depended on visual sightings, or radio signal direction finding. In WWI, when they started shooting at each other at longer ranges, sound ranging of artillery shots (with an early version of sonar, was added to RDF, but they depended on visual sightings to confirm their accuracy, so navies began experimenting with camouflage designs intended to misdirect observers.
The U.S. Navy Bureau of Construction and Repair began testing ship camouflage, colloquially referred to as “dazzle paint,” during World War I. The technique relied on reducing the contrast of the ship when viewed from the surface or the air from its surroundings as well as the contrast of one section of the ship from another.
The effect was intended to cause observers to misjudge the course, speed, and size of the ship. The designs included a moderate range of colors (hues), though post-war experiments would demonstrate that brightness contrasts were more important than color varieties.
Each side of the ship was painted with a different design, to add more confusion…
Port side-
Starboard side, SAME ship… with inserts for the upper works.
These next three are all starboard sides of different size/types of ships. The first is a ‘smaller’ cargo ship.
Starboard side, fuel/oil tanker. 
Starboard side, large bulk carrier.
And the Brits were also doing the same thing…
Ultimately, this was OBE with the advent of radar, but it is still an interesting use of trompe l’oeil. And it wasn’t limited to just merchant ships. Warships in WWI, especially the Brits, also used the technique to confuse their opponents.


The Blurb-