Alberich.
An interesting question was raised by falo to Simon if the pressurehull was covered by the Alberich rubber assuming the wooden casingdeck did not to be covered. My Asdic knowledge has become a bit rusty since my Asdic training course, but I guess the WW2 Asdic was based on the piezoelectro effect of quartzcrystal which then was transmitting acoustic pulses which were reflected by any object on its way. The sound "ping" was made audible to the human ear by mixing the frequencies in the Asdicset.
I am by no means an expert on the Albricht design, but I guess the pressurehull of a sub. is not the only surface which reflects the "ping", every surface like the pressure hull, casing, casing deck and tower would give a reflection. I should presume in order to have a sound reflectiondamping like the Alberich synthetic rubber layer, you should encase the whole sub. hence having Alberich cover on the surface encasing the sub.
Having looked at photos of the U-480 you can indeed see the she is covered by Alberich layer on the visible outer surfaces like pressurehull, casing and deck. The Asdic acoustic "pings" would be reflected by wood, thin steelplates (casing) as well as thick steelplates(pressurehull). Those parts like pipes, ducts, vents, valves and pressurehull inside the casing would be protected by the Alberich covered casing and deck.
At last, the Asdic reflection were very often disturbed by variation in the seawater salinity, temperatures etc. The submarines made use of this by launching a bubble decoy filled with magnesium pellets which reacted with the seawater creating bubbles giving a sonar reflection like a submarine.
Again I am not an expert on this item so just take it as an airing of my view.
Tore
