[Illustration: Figure 42--NINETEENTH CENTURY PROJECTILE FUZES.
a--Cross-section of Bormann fuze, b--Top of Bormann fuze, c--Wooden
fuze for spherical shell, d--Wood-and-paper fuze for spherical shell,
e--Percussion fuze.]
The eighteenth century fuze was a wooden tube several inches long,
with a powder composition tamped into its hole much like the
nineteenth century fuze (fig. 42c). The hole was only a quarter of an
inch in diameter, but the head of the fuze was hollowed out like a
cup, and "mealed" (fine) powder, moistened with "spirits of wine"
(alcohol), was pressed into the hollow to make a larger igniting
surface. To time the fuze, a cannoneer cut the cylinder at the proper
length with his fuze-saw, or drilled a small hole (G) where the fire
could flash out at the right time. Some English fuzes at this period
were also made by drawing two strands of a quick match into the hole,
instead of filling it with powder composition. The ends of the match
were crossed into a sort of rosette at the head of the fuze. Paper
caps to protect the powder composition covered the heads of these
fuzes and had to be removed before the shell was put into the gun.
Bombs were not filled with powder very long before use, and fuzes were
not put into the projectiles until the time of firing. To force the
fuze into the hole of the shell, the cannoneer covered the fuze head
with tow, put a fuze-setter on it, and hammered the setter with a
mallet, "drifting" the fuze until the head stuck out of the shell only
2/10 of an inch. If the fuze had to be withdrawn, there was a fuze
extractor for the job. This tool gripped the fuze head tightly, and
turning a screw slowly pulled out the fuze.
Wooden tube fuzes were used almost as long as the spherical shell. A
United States 12-inch mortar fuze (fig. 42c), 7 inches long and
burning 49 seconds, was much like the earlier fuze. During the 1800's,
however, other types came into wide use.
The conical paper-case fuze (fig. 42d), inserted in a metal or wooden
plug that fitted the fuze hole, contained composition whose rate of
burning was shown by the color of the paper. A black fuze burned an
inch every 2 seconds. Red burned 3 seconds, green 4, and yellow 5
seconds per inch. Paper fuzes were 2 inches long, and could be cut
shorter if necessary. Since firing a shell from a 24-pounder to burst
at 2,000 yards meant a time flight of 6 seconds, a red fuze would
serve without cutting, or a green fuze could be cut to 1-1/2 inches.
Sea-coast fuzes of similar type were used in the 15-inch Rodmans until
these big smoothbores were finally discarded sometime after 1900.
The Bormann fuze (fig. 42a), the quickest of the oldtimers to set, was
used for many years by the U. S. Field Artillery in spherical shell
and shrapnel. Its pewter case, which screwed into the shell, contained
a time ring of powder composition (A). Over this ring the top of the
fuze case was marked in seconds. To set the fuze, the gunner merely
had to cut the case at the proper mark--at four for 4 seconds, three
for 3 seconds, and so on--to expose the ring of powder to the powder
blast of the gun. The ring burned until it reached the zero end and
set off the fine powder in the center of the case; the powder flash
then blew out a tin plate in the bottom of the fuze and ignited the
shell charge. Its short burning time (about 6 seconds) made the
Bormann fuze obsolete as field gun ranges increased. The main trouble
with this fuze, however, was that it did not always ignite!
The percussion fuze was an extremely important development of the
nineteenth century, particularly for the long-range rifles. The shock
of impact caused this fuze to explode the shell at almost the instant
of striking. Percussion fuzes were made in two general types: the
front fuze, for the nose of an elongated projectile; and the base
fuze, at the center of the projectile base. The base fuze was used
with armor-piercing projectiles where it was desirable to have the
shell penetrate the target for some distance before bursting. Both
types were built on the same principles.
A Hotchkiss front percussion fuze (fig. 42e) had a brass case which
screwed into the shell. Inside the case was a plunger (A) containing a
priming charge of powder, topped with a cap of fulminate. A brass wire
at the base of the plunger was a safety device to keep the cap away
from a sharp point at the top of the fuze until the shell struck the
target. When the gun was fired, the shock of discharge dropped a lead
plug (B) from the base of the fuze into the projectile cavity,
permitting the plunger to drop to the bottom of the fuze and rest
there, held by the spread wire, while the shell was in flight. Upon
impact, the plunger was thrown forward, the cap struck the point and
ignited the priming charge, which in turn fired the bursting charge of
the shell.