When modern cruisers began in the powered era after about 1860, they were the heir's to the frigates of Nelson's day. However they were not descended from them .
They began with all-steel, steam ships.
They needed endurance for independent operations and protect trade routes, and speed to operate with the main battle fleet. For Britain they were principally a defensive weapon.
As time passed, they developed and were described in various ways. Usually in terms of the type of defensive protection.
The first type of protection was the construction of a full length protective deck about the waterline, sloping down to the edges to meet the ship's side and often additional protection was achieved by having coal bunkers above the slope of the protective deck. The objective was to allow the ship to stay afloat by having a raft below which was the ship's vital machinery and which would stay afloat no matter what damage was done to the upper part of the hull.
The protected cruiser was still vulnerable to damage below the protected deck from mines, torpedoes or explosion caused by fire reaching the magazines. The full length protective deck was common to most late Victorian cruisers and up until World War 1.
While it was preferable to stop shells from entering the ship, early armour was so heavy it was only possible to give early belted cruisers, narrow midships armoured belts which also had a protective deck. This caused caused a reaction against the Armoured Cruiser for several years. But with lighter armour of the same strength it became possible in the late 1890's to provide armoured side protection over 11ft in height from the bow to the machinery spaces. With varying thickness tapering towards the bow and stern. To give this side protection the protective deck was thinner than in a protective cruiser.
They had a light full length protective deck but extensive side armour.
These had three phases of armoured protection. Initially being conventional protected cruiser with a full length a full length protected deck on the waterline.
Later the protective deck was halved in thickness to allow a 2in belt along the sides.
Later still they had extensive side armour and a protective deck over machinery and steering spaces. Some later classes also had box armour around magazines.
They generally displaced less than 6,000 tons.
Although not used by the Royal Navy, the term heavy cruiser was often used for ships greater than 6,000 tons. After the Washington Treaty, heavy cruisers were usually near the cruiser upper displacement limit of 10,000 tons.
Cruisers after WW1
After world war 1, long range plunging fire, aircraft and torpedoes made it essential that both vertical and horizontal protection be provided. But with displacement limited by treaty it was impossible to give armour protection overall. The solution was to provide armoured boxes covering boiler and machinery spaces, later extended fore and aft to cover magazine spaces and the ship's vitals, all covered by extensive bulkhead subdivision.
Some also incorporated anti-torpedo bulges.
This page last edited -
31 January, 2013.
Copyright © Ian M King, except where otherwise indicated.