> if you can't defend a mobile ocean-going fortress, what can you defend? Underground bunkers (I believe Sweden has a decent history of converting caves into a

> if you can't defend a mobile ocean-going fortress, what can you defend? Underground bunkers (I believe Sweden has a decent history of converting caves into aircraft hangers). Just as we don't really have conventional fortresses on land any more, only trenches and bunkers, as munitions get better we're reaching a point where the only way to keep anything safe is to bury it.