Their turret strength is 3 as part of their basic profile and point cost. This does not affect their ability to take an additional turret as part of Battlefleet Bakka.
The specifications for these vessels relied heavily on a degree of compartmentalization that proved too cumbersome for later ship designs. However, this results in the Endeavour light cruisers getting a +1 to their dice roll when defending against a boarding action.
Options
May increase the prow armour to 6+ for no additional cost. However, if this option is taken, the turning radius of these vessels is reduced to 45 degrees.
If the prow armour is increased, the ship may also take a power ram for +5 points, if it is part of an Imperial Navy, Adeptus Mechanicus, Inquisition, or Rogue Trader fleet list. This does not count as a separate refit. Ships so equipped impart one automatic hit during a successful ram on a target vessel before rolling for hits inflicted.