Hi Frank

The germans began experimenting with a system of textured synthetic rubber (Oppanol) panels known as Alberich.The intent was to cover the entire outer surface of a U-Boat with 4mm thick panels.
The experiments began in 1940 when the tiny U11 was coated with Alberich panels.Tests showed that at best Alberich reduced sonar pulse reflectance by 15 per cent at periscope depth, with the percentage of absortion varying with depth.
Despite these somewhat dissapointing findings, the tests continued in 1941 with the covering of U67.Tests on this boat had mixed results.
Any benefits gained from were offset by the noise generated by panels coming loose as the U-Boat moved.In a trial run between Norway and France U67 lost 60 percent of the panels.Trials continued on u67 and
on UD4 (ex O-26), but were eventually discontinued due to the inability to overcome the adhesion problems.
Curiously actual navies are experiencing some problems with the
adhesion of the rubberized tiles, designed to reduce the sonar signature of its latest submarines.


Best Regards