However, the success of the _Princeton_ as a ship was so pronounced that money was appropriated from time to time for others designed much as she was until the navy had six screw frigates--the _Niagara_, the _Roanoke_, the _Colorado_, the _Merrimac_, the _Minnesota_, and the _Wabash_; six screw sloops of the first class--the _San Jacinto_, the _Lancaster_, the _Brooklyn_, the _Hartford_, the _Richmond_, and the _Pensacola_, besides eight screw sloops of the second class, of which the _Iroquois_ was a type, and five of the third class, of which the _Mohawk_ was a type. There was also a screw frigate on the stocks at the Portsmouth, New Hampshire, dock-yard. The guns that these ships carried, when compared with those of the war of the Revolution, were quite as interesting as the ships themselves. [Illustration: U. S. Frigate _Pensacola_ off Alexandria. _From a photograph taken in 1865._] The prejudices in the way of improving great guns were not only strong, but they were founded on experiences that were seemingly convincing beyond peradventure. For instance, under Charles V a cannon was cast at Genoa that was fifty-eight calibres long; that is, it was of about six inches diameter of bore and twenty-nine feet long. When fired, its ball of thirty-six pounds weight had less range than an ordinary twelve-pounder. So they cut off four feet of the gun and found that its range increased. Cutting off three feet more still further increased the range, as did another cut of six inches--“which shows,” says Simpson’s text-book on gunnery, printed in 1862, “that there is for each piece a maximum length which should not be exceeded.” So that dictum stood in the way of arriving at the design of a gun like the modern rifle, that would really give the greatest possible range to a projectile. Then, the distribution of the metal in the cannon with which Arnold fought on Lake Champlain seems now ridiculous. One must needs see a picture of the old gun beside one of the guns as developed just previous to the Civil War to realize the difference; but it may be said that, with the bell-shaped muzzle and the “rings” and “reinforces,” the old gun in outline had as many ups and downs as some step-ladders, while the cast-iron weapon of 1860 was as smooth and symmetrical as the hull of a Yankee clipper. [Illustration: A Twelve-pound Bronze Howitzer--the First One Made in the United States. _From a photograph of the original at the Brooklyn Navy Yard._]