Report of the Navy Department Bureau of Ordnance

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NAVY DEPARTMENT
BUREAU OF ORDNANCE

WASHINGTON, D. C.

To: The Chief of Naval Operations.
Subject: Smoke producing shell Edison design.

1. Mr. Edison has proposed the use in antisubmarine warfare of a shell filled with a mixture producing smoke. These shell to be used essentially as defensive shell, to be thrown between a vessel and a submarine for the purpose of creating a smoke fog or screen, preventing the observation by the submarine of the vessel's movements and conclusively preventing accurate gunfire from the submarine against the vessel.

2. The principle is undoubtedly valuable, and the Bureau has for some years been experimenting in the endeavor to obtain a satisfactory smoke producing shell.

3. Mr. Edison has performed certain experiments which lead him to believe he has obtained a satisfactory shell for the purpose. This shell is loaded with sulphuric acid in which is absorbed a certain proportion of sulphuric anhydride. It is understood that his shell has been brought to the attention of the President of the United States, the Secretary of the Navy and the British Admiralty.

4. Before commenting on Mr. Edison's shell, it may be advisable to show the conditions which must be fulfilled by any smoke producing shell for use in naval warfare.
(a) The shell must be loaded with materials which are safe during storage aboard ship and which can withstand the shock of gunfire.
(b) The shell filler must of itself be sufficiently explosive to burst the shell when ignited by a fuse, or it must be practicable to introduce a separate bursting charge into the shell.
(c) The smoke producing material must be such that it will not be readily absorbed by water.5. Requirements (a) and (b) are self evident. Requirement (c), hoever, needs some explanation. Obviously, for the purpose of laying a smoke screen between a vessel and the target of its guns, impact with the target ship can not be counted upon as a means of explosion of the shell. Consequently, the shell must be exploded in one of two ways; (1) in air, by the action of a time fuse; (2) or on impact with water, at some point short of the target.

(1) The ideal conditions of the use of smoke shell would permit bursting shell in air close to the surface of the water, such burst spreading the smoke immediately above the surface of the water. Such ideal conditions, however, can not be found. For such action it would be necessary to know precisely the range and the time of flight to be expected under the prevailing atmospheric conditions. In addition, absolutely accurate time fuse action would be necessary. With the present types of time fuses this last is impracticable, as the best that can be counted upon is a variation of.4 seconds or 200 yards in range, or at an angle of fall of 15 degrees 150 feet in height. Consequently, failing the impossible ideal conditions the result of the attempt to use smoke shell exploded in air by a time fuse would be a series of smoke clouds distributed along the arching trajectory of the shell, and effective at the surface of the water only in case of a very lucky, rather than very accurate, shot.

(2) Impact with water, however, furnishes a ready and accurate means of exploding the shell in direct line between the ship and the target vessel. Impact fuses will readily explode shell on contact with water. The curve of the trajectory interposes no objectionable features, since the shell is not exploded until it reaches the surface of the water, in the plane of vision between submarine and vessel. Thus, automatically, the difficulties of range and timing are obviated and all that becomes necessary is to land the shell in line with the target, on the "near" side thereof, a very simple ballistic performance in comparison with the complicated and accurate firing required for the shell exploded in air. On impact with water, a sensitive fuse will explode the shell in a time estimated as not greater than .01 to .1 second. During this time, however, the shell has penetrated beneath the surface of the water to a certain distance, and on its explosion its contents must to some extent pass through the water before again reaching the atmosphere.

6. From the above, the necessity of requirement (c), that the shell filler should be of material not absorbed by water, is apparent. The only practicable smoke shell is one which can be fired to explode on impact with water. On such impact it is below the surface of the water at the moment of explosion and the products of its explosion, in order to reach the atmosphere and form smoke clouds, must be such as not to be adsorbed by water.

7. Returning to the consideration of Mr. Edison's shell. He proposes a shell loaded with concentrated sulphuric acid saturated with sulphuric anhydride, Photograohs attached to his correspondence display considerable smoke effect over land. As noted above, however, smoke producing materials non-absorbable in water are necessary. Sulphuric acid and sulphuric anhydride have a very strong affinity for water. It is not believed possible that shells with this material exploded on contact with water will produce a satisfactory smoke screen. For the reasons noted above it is deemed impracticable to use time exploded shell to produce a smoke screen. Consequently, the shell filler proposed by Mr. Edison is deemed unsatisfactory for naval use.

8. In addition to these objections it would appear that the use of sulphuric acid, highly concentrated, would be dangerous in a shell containing, necessarily, other explosives to burst the shell. This difficulty, however, might be obviated, but the primary objection of absorption by water is considered insurmountable for this material.

9. The type of shell body proposed by Mr. Edison in his letter of August 15th appears generally satisfactory. It differs so little, however, except in length, from the standard shrapnel shell, that the Bureau considers that for experimental purposes the shrapnel shell would prove adequate.

10,. The Bureau does not doubt the evidence of Mr. Edison's photographs that a very satisfactory smoke fog can be obtained over land with the proposed chemical, but it is convinced that the chemical in question is impracticable for use as a shell filler for smoke producing shell to be fired over water.

11. The Bureau does not recommend experimental firing of this oleum shell, believing that the shell is dangerous in loading and is essentially valueless in performance for naval use.

12. The Department is advised that the Bureau is continuing its experiments in the development of a smoke shell satisfactory to meet the conditions prescribed above as essential.