Concussion fuzes and spherical shells Early use in the French navy. Dr. BALLIET J.M. – 2004 - rev. 2013
The cannon ball was the primary projectile in the navy even if the spherical explosive shell was used in all types of cannons in the 1830s French navy. A classical time-delayed wooden fuze was used. In 1837-1938, the French navy artillery commission (Commission de Gâvre) made some tests to establish the combustion delay in the wooden fuzes. A "Canon-obusier de 30" of Paixhan's design was used for the trials. The conclusion were quite appealing: irregular and inconsistent function. At that stage, these wooden fuzes were thought to be pretty ineffective against ships and since several years, it was given thought to an concussion fuzed [spherical] shell. But the solution wasn't at hand: the impact did occur on any place of the projectile. The colonel Jure, belonging to the French marine artillery, made some studies on this case for ten years and, in 1834, his fuze system was adopted by the French navy. It used an iron stem, which under the shock came to strike a starter. Even if theoretically the fuze had to be effective at any point of impact, the author had given some thought as to maximize the chance of impacting on the fuze head: an iron rope was attached to the spherical projectile! The results were rather hazardous: premature explosion in the cannon bore, lack of reliability on impact… Promptly some studies were conducted in view to overcome the shortcomings. These improvements weren't made by the author but y a member of the 1833's artillery commission, the lieutenant Billette. Soon adopted under the name "Projectile Billette" a used a principle so secret that even the French navy, which adopted the projectile didn't know how the shell and fuzes were fabricated and it's exact effectiveness!
Fig. 1 Lieutenant Billette’s impact fuze
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Rapidly, a conflict as to the intellectual properties developed between Billette and Jure and new trials were made until Billette's shell was officially accepted for on board use. It was so secret that Billettes was the only one to construct the fuze and even the transportation of the shells from one naval port other than Brest required that a brick was put under Billette's personal command. In 1847, Billette died after two years of illness since the fabrication of the fuze was interrupted. Only his widow had a full description of the fuze system but the negotiations with the French navy weren't successful in view of the exorbitant demands of Billette's wife.
Fig. 2 Wooden fuze for spherical shells
A captain Bourguignon was soon appointed to study the fuze and to do some reverse engineering. New trials were successfully conducted in 1848. But like Bilette, this officer considered tis fuze as his private property and kept closely his secret until he died in 1853! As in the earlier case, the French navy had no full knowledge of the fabrication process and it was only with the adoption of the rifled artillery system that this farce ended. In fact were theses spherical concussion spherical projectiles effective in spite of all their mysteries? Probably not since trials proofed that spherical shells with an ordinary wooden fuze often detonated on impact. This was due to the shock determining some slits in the fuze length which gave passage to the flame. The shells with ordinary fuzes were in fact real concussion primed shells!
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