76 ANNUAL OF SCIENTIFIC DISCOVEKY. 



CAPT. DAIILGEEN ON IKON-PLATED SHIPS. 



The following letter was addressed to the chief of the U. S. Bureau 

 of Ordnance and Hydrography, under date of December 10th, 1860, 

 by Capt. John A. Dahlgren, U. S. N., the well-known inventor of 

 the " Dahlgren Gun," and other valuable improvements in ordnance. 

 From such an authority the views expressed have much of interest. 



SIR, The earnest attention now given by naval authorities to the 

 armature of ships of war, and the enormous expenditure which Eng- 

 land and France are incurring in building ships of this description, 

 induce me to recall the attention of the bureau to the suggestions 

 made by me on this subject several years ago. 



In 1852, after a series of practice on the hull of the United States 

 steamer Water Witch, principally with nine-inch shell at five 

 hundred yards, I made a report of the facts to the bureau, and in 

 conclusion affirmed the possibility of guarding vessels against the 

 dangerous action of heavy shells. The following passages may be 

 referred to as more particularly applying to this subject : 



" These conclusions, when combined, are suggestive of the follow- 

 ing propositions : 1st, that the sides of a vessel may be so protected 

 by iron frames, or plates, as to make it nearly certain that shells will 

 break by impinging thereon. The effect of the explosion will be 

 almost nullified in this way. 



" Query: Will the weight of the metallic material so used consti- 

 tute a serious objection in view of the importance of avoiding the 

 damage that may result from suffering the risk of a large shell's ex- 

 ploding in the frame or about the decks? Experiment will best 

 determine this. 2d. By interposing the coal stowed aboard steamers 

 between the sides and the motive power, there is a very great prob- 

 ability that, in connection with iron ribs or plates on the side, the 

 boilers and machinery may be protected against any ordinary casu- 

 alty from shells, at least during the period common to sea engage- 

 ments. 



" The formidable power of shells has long engrossed attention, 

 and the tendency to their use is evidently on the increase. If only 

 a moderate portion of their destructive effects be realized, there is 

 every reason to look for more speedy results in sea engagements than 

 have yet been witnessed ; and it would be very desirable on many ac- 

 counts to diminish, if possible, the capacity of this means of offence, 

 particularly as regards sea steamers, the value of which has been ma- 

 terially affected by the liability of their motive power to derange- 

 ment by projectiles ; this consideration has exercised a controlling 

 influence in the character of their armament, which is designed to 

 operate at distances far greater than the pieces ordinarily found in 

 broadside. So far as shells are concerned, even of heavy calibres, 

 I am clearly of opinion that their destructive effects may be nulli- 

 fied, more or less, by the use of iron ribs or plates, and the proper 

 disposition of the coal which every steamer has ordinarily at dispo- 

 sal. 



" And if the results here truly represent those which will occur in 

 the average, the motive power of a steamer will be exposed to no 

 greater risk from shells at moderate distances than that of a sailing 



