Ice,
Here's a couple of books which might interest you:
American Seacoast Defences; A Reference Guide (2nd Ed.) by Mark Berlhow. 632pp Softback, CDSG Press.
The Military History of Boston's Harbour Islands by Gerald Butler. Arcadia Publishing 2000
I also found this new site on the
Stalin Line in Belarus.
And this forum dedicated to fortifications-
web page