They were designed and built to be used as local defence ships, and it was not expected that they would ever need to be deployed far away from their bases.

It was therefore possible to design them without sails or rigging and dependent only upon their engines, with a resulting limitation in their effective range.

The absence of masts and rigging allowed more weight to be worked into the ship's armour.

This also meant it was possible to arm the ships with two gun turrets, one fore and one aft, which had wholly unobstructed fields of fire over the bow and stern, and on wide arcs amidships.

The turret armament provided an additional advantage of allowing the ships to have a low freeboard.