Design
Shannon was built in response to two threats. The instructions of the Admiralty to the designer, Nathaniel Barnaby, were to design an ironclad "capable of competing with the second class Ironclads of foreign navies". This meant in particular the ten French armoured corvettes of the Alma and La Galissonnière classes, though the ironclads of the smaller navies of Asia the Americas also featured. The British counter to these ships were the Audacious and Swiftsure classes of second-class ironclad of the 1860s. Shannon 's design was in the lineage of these ships, though the tactical landscape was changing. At the same time as Shannon was being planned, the Russian navy launched the first armoured cruisers, General Admiral and her sister Gerzog Edinburgski. These ships were intended for the traditional cruiser mission of commerce raiding, but were armoured and armed on the same scale as a second-class ironclad. The existence of these ships mean that Shannon was now expected to act as a counter to them, and perform the commerce protection missions which had previously been the preserve of unarmoured cruisers, most recently the Inconstant.
Shannon was armed with two 10-inch guns in armoured embrasures facing towards the bow, six 9-inch guns on the open deck amidships, and a seventh 9-inch gun facing astern. The astern gun could be fired from either of two unarmoured embrasures, one on each side of the ship. She was also equipped with an unusual detachable ram, which was meant to be removed in peactime to reduce the risk of accidentally ramming another warship. The ram was supposed to be stowed on board and attached in wartime; however this proved to be a very impractical arrangement.
Shannon was armoured in an unconventional manner. An armoured belt 9 ft tall and between 9 in and 6 in thick ran for most of the length of the ship, but stopped 60 ft from the bows. Above the belt was an armoured deck 1.5 in thick, the first such armoured deck on a British warship. At the point the belt ended, a 9 in armoured bulkhead ran across the ship, the top of which formed the embrasures for the 10-inch guns on the upper deck. From the bottom of this bulkhead, a 3 in thick armoured deck extended to the bow, at a level 10 ft below the waterline. The space above this forward armoured deck was filled with coal bunkers and stores to limit any flooding.
The 9-inch guns were unarmoured (though the armoured bulkhead did protect them against raking fire from ahead) and would have been very exposed in combat. In an action, it was hoped to attempt to ram the enemy while firing with the forward guns and preparing the 9-inch broadside. The crews could then retreat into the armoured part of the ship. If the ramming failed then the guns could be fired electrically as Shannon passed her target.
Shannon could use both sail or steam power. While steam was much preferred for combat, sail propulsion was considered vital for a ship intended to operate worldwide. She was given a lifting screw in order to increase her efficiency under sail, the last Royal Navy warship to be so equipped. She had three masts, and was initially given a ship rig with 24000 ft² of sail, a point insisted on by the Director of Naval Operations, Capt. Hood. In service, this was reduced to a barque rig with 21500 ft². She was equipped with Laird two-cylinder compound engines, the high-pressure cylinders being 44 in in diameter and the low-pressure cylinders 85 in. Steam came from eight cylindrical boilers at 70 lb pressure. Her design top speed was 13 knots (24 km/h), but her best actual speed was 12.25 knots (23 km/h). To reduce fouling, she had zinc and wood sheathing on her hull.
Read more about this topic: HMS Shannon (1875)
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