Hi,
Came across an interesting web page with some nice photos concerning the Italian Tenth Flotilla MAS:
http://www.regiamarina.net/xa_mas/history/origin_us.htm
This link takes you an English version. Clicking on the XA MAS button on the top of the page takes to 12 pages including a page noting a planned attack on New York City. The photos alone are worth the look.
English sources are easier to find. This is one of many examples for British Frogmen:
http://www.divingheritage.com/torpedokern.htm