Ship Cover for the Iris class despatch vessels HMS Iris (1877) and HMS Mercury (1878). The documentation covers the initial design proposal [including a comparison with HMS Volage (1869)], specifications and a fairly lengthy justification for the new ships, stability calculations, statements of hull dimensions and weights, armament and ammunition allowance, crew complement, and masting, rigging and sail arrangements. Further papers relate to the steaming and manoeuvreing trials conducted with HMS Iris shortly after her commissioning. The date range begins in November 1874 at the beginning of the design process and concludes in May 1906, shortly after Mercury's conversion to a submarine depot ship.