Notebook #7
Wonder why the RN didn't leave at least one battleship further South?
Same reason that the Krigsmarine wanted to move there boats out of France. In range of German bombers and torpedo boats. Also two or more Battleships would have been required to deal with the German ships.
Linguofreak #8
Yes they can and have been used offensively, In both world wars they where used to block ships from entering or leaving port or area. And to limit movement of hostile fleets by requiring minesweepers to clear passages.
Notebook #7
Strange how we are still finding bombs from WWII but not mines? Guess they have all sunk and detonated on the sea floor?
Most if not all naval mines post 1900 had/have timing devices to arm them after the mine layer has finished its work and left the area. Modern and late WW2 mines had deactivating timers too, they usually just detonated them but some used devices to sink them for later retrieval.
Naval mines still are limited by the depth of water they are layed in, most if not all the mines layed in WW2 where layed in less than 100m of water which meant removing them was relatively easy, as everyone kept good documentation on where the mines where layed. No one wanted to run into a mine especially a "friendly" one.
The Royal Navy no longer use naval mines, but do have training mines to keep the minesweeper and ordinance disposal teams skills.