It should read:
4) When a battleship has a damage marker its firepower is reduced by one i.e.
a) A battleship with one damage marker, hits on a roll of 3
b) A battleship with two damage markers, sinks
c) An Aircraft carrier with a damage marker sinks
d) A cruiser with one damage marker sinks
all ships thats take one hit sink is the rule
the BB can take 2 hits before it sinks.
If you want to make all the units take 2-3 hits, that will be a big change