Can rubber make things invisible?

In 1944, the Germans discovered rubber worked well in absorbing sonar frequencies, so they covered a submarine with an experimental synthetic rubber coating.  If sonar was pointed at the target, it yielded no return data. So the sub successfully dodged Allied patrols in the Atlantic until it surrendered at the end of WWII.

The Americans learned the Russians were using this early version of "stealth" technology in the 1950s when the U.S. Navy "bumped" into a Soviet submarine and some of the rubber stuck to the American sub's hull.

If you want to see for yourself the "invisible" rubber submarine, a former Soviet Juliett 484 is on display in the harbor of Providence, Rhode Island. 

From a distance, the outer skin looks like the result of a bad weld job. But closer inspection reveals the 300-foot sub is covered in 1/2-inch thick rubber tiles of various shapes and sizes. Bolts were used to attach the irregularly shaped rubber tiles to the sub's hull.