It is proper to explain here that there was one feature of the earlier plans which were submitted to Napoleon III. in 1854, which he did not embody in the "Monitor," and which, indeed, was omitted from all published plans and descriptions of the system given out in former years. This was a system of submarine or subaqueous attack, which, he states in a letter to John Bourne, had attracted his attention since 1826. The time now seemed ripe for the presentation and development of this idea, and he accordingly developed his designs for a torpedo, and for a method of firing it under water from a gun carried in the bow of a boat, and suitably opening to allow the discharge of the torpedo projectile. This was Ericsson's so-called "Destroyer" system, and was embodied finally in a boat called the "Destroyer," which he built in company with his friend, Mr. C.H. Delamater, and with which he carried on numerous experiments. In the end, however, the system did not commend itself to the naval authorities, and the "Destroyer" was left on her designer's hands, an instance of difference of opinion between Ericsson and those charged with the duty of naval administration, and with no supreme test of war to provide opportunity for the determination as to which were the more correct in their judgment. With the "Destroyer," and his work in connection with her, closes the record of Ericsson's connection with the advance in naval construction. During these later years of his life it must not be supposed that he was less busily occupied than in earlier life. His was a nature which knew no rest, and to the last day of his life he was literally in the harness. Only brief mention however can be made of some of the more important lines of work which interested the closing years of Ericsson's life. 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.