A shallow-draft, fast, low-profile vessel, she was designed to penetrate enemy harbours at speed and sink anchored ships.

[3] Designed by Nathaniel Barnaby primarily as a protected torpedo boat, the ram was provided very much as secondary armament.

Leading on from this, in the mid-1870s Barnaby and his assistant J Dunn proposed a fast cigar-shaped vessel with five submerged torpedo tubes and protected by 2 inches of armour over the deck.

It hinged upwards to open, and considerable effort went into selecting the best hydrodynamic design through model testing since its size and location were found to have a major impact on the ship’s performance.

The principal object of this was to test tactics for a possible attack on Kronstadt Harbour in the event of the threatened war with Russia.

Booms and nets (to catch propellers) were laid across the channel behind Bereshaven, along with small observation mines and the area covered by machine guns and torpedo boats.

[9] Despite this success, no further vessels were ordered by the Royal Navy, possibly because the development of quick-traversing and quick-firing guns as she entered service had rendered the concept behind her design less practical.

[4] When she was designed, the only guns capable of penetrating her armour were too slow to train and fire to have much chance of hitting such a fast-moving ship, but by the time that she entered service a few years later, this was no longer true.