Not all lightships were turned off
Indeed the British kept a few going to aid convoy navigation
Same with the US
And by the same reasoning they helped the uboats too
None were ever sunk by uboats
http://www.uscg.mil/hq/g-cp/history/...ion_Index.html gives a list of US lightships with dates for each area
The Uk ones are a lot harder to pinpoint but
http://www.feuerschiffseite.de/u-englgb.htm gives some info
Dutch ones here too
http://www.lichtschepen.com/productssimple13.html