Some books on this topic:

"Marine-Kleinkampf-Mittel" (Harald Fock, 1996. 216pg, german text. ISBN 3-930656-34-5 )
"Weapons of Desperation - German Frogmen and Midget Submarines of World War II" (Lawrence Patterson, 2006. 292pg, english text. ISBN 1 86176 279 8 )
"Midget Submarines of the Second World War" (Paul Kemp, 1999. 134pg, english text. ISBN 1 84067 521 7 )
"War at Sea 21 - Midget Submarines and Human Torpedoes - Part 1" (2005, 52pg)
"War at Sea 22 - Midget Submarines and Human Torpedoes - Part 2" (2005, 52pg)
"War at Sea 23 - Midget Submarines and Human Torpedoes - Part 3" (2005, 52pg)
"War at Sea 24 - Midget Submarines and Human Torpedoes - Part 4" (2005, 52pg)

The last four are russian tiles, and I have no way to interpret further information in regards of authour and publisher... They are interesting though, as they offer more/ different photos than the other books.



A couple of titles covering british midget-submarine operations are also worth mentioning:

"Underwater Warriors" (Paul Kemp, 1999. 264pg, english text. ISBN 1 86019 991 7 )
"Above Us the Waves - The Story of Midget Submarines & Human Torpedoes" (C.E.T. Warren & James Benson, 1953. 260pg, english text. ISBN 1-84415-440-8 )