"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, and 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 meant 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".