For pretty good (free) electronic basic learning manuals, the Navy Electricity and Electronics Training Series 1998 is available on line in PDF format.
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NEETS is also available, in print, on line, from Barns and Nobel for $4 (new) and at Alibris for $2.30 (used).
The site is also a treasure trove of WW2 historical technical and tactical information, destroyers, battleships, submarines, and weapons systems. With links to more sites with more eclectic naval warfare information.
Even has a link to "THE SUBMARINE COMMANDER'S HANDBOOK
("U.Kdt.Hdb.") 1942 New Edition 1943
This is a secret subject according to paragraph 88 of the "Reichsstrafgesetzbuch" (Reich Code of Criminal Law) (Edition of 24th April 1934). Misuse will be punished according to the provisions of the said Paragraph, insofar as other penalties do not apply.
High Command of the Navy
"Waterborne Underwater Hull Cleaning of Navy Ships, 2002" sounds like a real page-turner.