The _Polyphemus_ performed little useful service; her life on the Navy List was short; and she is always spoken of as a “failure.” Officers who served in her were, however, invariably enthusiastic about her, and had war occurred during the time that she was in existence there is no telling what she might have accomplished or how profoundly she might have affected naval construction. In essence the _Polyphemus_ was a semi-submerged craft, those parts of her which were above water being merely a light superstructure for the accommodation of her crew in peace time. She was of 2,640 tons displacement, length 240ft. between perpendiculars, beam 40ft., and a normal mean draught of 20ft. In form she was cigar-shaped, plated with 3-inch armour on the upper part of her curved sides. With 5,520 I.H.P. she had the then very high speed of 17.8 knots. She carried 300 tons of coal, sufficient for a nominal radius of 3,400 miles at economical speed. Her principal feature, however, was the fitting of five submerged tubes, one in the bow the others on the broadside. For repelling a torpedo attack she carried six 6-pounders and a couple of machine guns. [Illustration: POLYPHEMUS. ALARM. KATAHDIN. SOME FAMOUS RAMS.] It is here of interest to relate that some years later the U.S. Navy created a species of _Polyphemus_ imitation in the “ram” _Katahdin_. To a certain extent they had anticipated her likewise in the _Alarm_, 720 tons, launched in 1873, which carried a 15-inch smooth-bore gun _under water_ in her ram, and the _Intrepid_ (launched 1873), of 1,123 tons, of which no details ever transpired, and it may be said that she was “strangled at birth.” But the _Polyphemus’s_ ancestry is undoubtedly American. The _Katahdin_ (first produced as the “ram” _Ammen_) was not launched till 1893. She was of 2,050 tons and seventeen knots, and having no torpedo tubes, being a “ram” pure and simple, exactly reproduced the Sartorious-Barnaby idea. She soon disappeared from the U.S. Navy List, and she never did anything. She doubled the armour of the _Polyphemus_, whilst lacking her torpedo armament. Since then, the idea has found expression in three small U.S. “semi-submerged” boats, with the torpedo as their main armament; but these three boats never got beyond the “designed” stage. No other nation ever exhibited the least interest in the _Polyphemus_ idea.