The particular one of these three especially intended for this peculiar emergency was a ship of entirely novel design, made by the celebrated inventor John Ericsson, a Swede by birth, but American by adoption—­a man who combined great original genius with long scientific study and experience.  His invention may be most quickly described as having a small, very low hull, covered by a much longer and wider flat deck only a foot or two above the water-line, upon which was placed a revolving iron turret twenty feet in diameter, nine feet high, and eight inches thick, on the inside of which were two eleven-inch guns trained side by side and revolving with the turret.  This unique naval structure was promptly nicknamed “a cheese-box on a raft,” and the designation was not at all inapt.  Naval experts at once recognized that her sea-going qualities were bad; but compensation was thought to exist in the belief that her iron turret would resist shot and shell, and that the thin edge of her flat deck would offer only a minimum mark to an enemy’s guns:  in other words, that she was no cruiser, but would prove a formidable floating battery; and this belief she abundantly justified.

The test of her fighting qualities was attended by what almost suggested a miraculous coincidence.  On Saturday, March 8, 1862, about noon, a strange-looking craft resembling a huge turtle was seen coming into Hampton Roads out of the mouth of Elizabeth River, and it quickly became certain that this was the much talked of rebel ironclad Merrimac, or, as the Confederates had renamed her, the Virginia.  She steamed rapidly toward Newport News, three miles to the southwest, where the Union ships Congress and Cumberland lay at anchor.  These saw the uncouth monster coming and prepared for action.  The Minnesota, the St. Lawrence, and the Roanoke, lying at Fortress Monroe also saw her and gave chase, but, the water being low, they all soon grounded.  The broadsides of the Congress, as the Merrimac passed her at three hundred yards’ distance, seemed to produce absolutely no effect upon her sloping iron roof.  Neither did the broadsides of her intended prey, nor the fire of the shore batteries, for even an instant arrest her speed as, rushing on, she struck the Cumberland, and with her iron prow broke a hole as large as a hogshead in her side.  Then backing away and hovering over her victim at convenient distance, she raked her decks with shot and shell until, after three quarters of an hour’s combat, the Cumberland and her heroic defenders, who had maintained the fight with unyielding stubbornness, went to the bottom in fifty feet of water with colors flying.