Fortifications
Channel Islands Occupation Society- www.ciosjersey.org.uk
Fortress Study Group- www.fsgfort.com
Shorncliffe Redoubt Preservation Society- www.shornclifferedoubt.com
Petrovaradin Fortress, Serbia- www.peterwardein.com
Subterranea Britannica- www.subbrit.org.uk/
Fortress Military- http://groups.msn.com/FortressMilitary
Site O- www.siteo.net/
Hitler's Atlantic Wall- www.bunkersite.com/
Pillboxes UK- www.pillboxesuk.co.uk/
UK Fortifications Club/Pillbox Study Group- www.ukfortsclub.org.uk/
The Defence of Britain Database- http://ads.ahds.ac.uk/catalogue/specColl/dob/