In connection with his naval designs, he devoted much study to the improvement of heavy ordnance, both as to the gun and its mounting.  In particular, his mounting of the guns in the “Monitor” was quite original, and the friction arrangement for absorbing the recoil was a great improvement over methods then in use, and served as a model for many copies and adaptations of the same principles in later years by other designers.  In 1863 he also designed and built for the acceptance of the Government a forged 13-inch wrought-iron gun.  While his design was an advance on those of the day, the demands on the makers of iron forgings were more than could be successfully met, and the gun developed some slight cracks in the test, which prevented further developments on this line.  Ericsson always maintained that the tests to which this gun was submitted were unfairly severe, and he showed how the defects could be remedied by a steel lining.  But the Naval Bureau of Ordnance insisted that this should be done at his own expense, and as he had already lost some $20,000 on the gun, he was unwilling to proceed farther, and the matter was allowed to lapse.

Throughout his entire career the improvement of the steam-engine occupied a large share of Ericsson’s attention, and in particular was this the case in connection with his naval designs.  From the “Princeton,” in 1841, to the “Destroyer,” in 1878, there succeeded one long series of types and forms of steam-engine, each in his opinion the best adapted to the circumstances of the case.  Naturally, opinions differ, and he was brought into competition with other able engineers, and his designs were often called into question or subjected to criticism.  In 1863, in competition with Chief Engineer Isherwood of the navy, engines were designed for twin ships, the “Madawaska,” afterward known as the “Tennessee,” and the “Wampanoag,” afterward called the “Florida.”  This was a battle royal of types and modes of application of the power of the steam-engine to the propulsion of ships.  The result was a victory for Isherwood, although the “Madawaska,” which was first subjected to trial, made a speed higher than any warship at that time afloat.  This was exceeded by the “Wampanoag” a short time later; but neither engine was of an enduring type, and after a time the machinery of the “Madawaska” was removed, and she was repowered with a later type of machinery, and long did service as the “Tennessee” in the list of wooden frigates of the navy.  The “Florida” was too expensive to maintain in commission, and the special circumstances which had called her into existence having passed by, she was laid up at New London, and never again saw active service.