The Sun.
London, England, 1867-05-24 00:00:00

The Chalmers Target at Vincennes.

Some important experiments were made on Mon-
day at Vincennes in the presence of various distin-
guished officers of the Artillery and Marines in the
French and English services. One of the main ob-
jects was to test the Chalmers system of backing
armour-plates. Two targets were erected—one on
the Chalmers plan, and the other representing a
section of an ordinary French ironclad ship of war.
The superficial dimensions of the targets were the
same—about 17ft. by Bft ; and they were placed
side by side in a nearly vertical position. The French
target was protected by two wrought-iron plates of
71 inches, but the plates on this as well asout the other
covered a portion of the surface only, bout the
by 6ft. The Chalmers target had a front plate of
5i inches ; behind which was the compound back-
ing of alternate layers of iron and timber ; the
laminae of iron being a foot wide and over i-inch
thick, the timber being of the same width, and 6
inches in thickness. These layers were, before be-
fore being attached to the target, riveted together
in blocks of three plates of iron and two planks of
timber ; the whole backing finally resting against a.
second plate of Finch iron covering the upright
timbers of the target. The vertical timbers and
inner planking of both targets were alike, and both
were supported in the rear by iron knees and a
strong diagonal frame of timber. The two were, it
would seem, intended to have been fired at alter-
nately, but the actual practice made was against
the Chalmers target only. The rounds were fired
from a 9-inch 12-ton Armstrong gun, throwing 250
pound steel shot with Palliser ogival form of head ;
some were with full charges of 431 b. of English
powder, and some with reduced charges. Two
shots penetrated, one stuck, and three failed
to get through the out plating.
These experiments seem to deserve attentive con-
sideration.. Strict comparison with those recently
made against combined steel and iron plates at Shoe-
buryness is hardly possible, h•cause the plates there
were unsupported, and the effects of the Palliser
missiles upon them was more of a simple punching
nature. Still when we regtrd the fact that in our
experiments a 7in. gun was used against 7in. plates,
and just penetrated, or rather stuck, in gelled with
e two best
plates (Messrs. Cammell's), when prop
151 b. of powder, we must accord some very con-
siderable value to Mr. Chalmer's backing when,
with its assistance, a 531 n. plate can be made to keep
out the larger and heavier shot from a 9in. gun.
The rule for punching plates is well known—
namely, a di,uueter of shot slightly larger than the
thickness of the plate, and the greater the margin.
between the diameter of the shot and the thickness
of plate the more the difference tells in favour of
the penetrative action of the shot. We have the
impression that a 51in. Millwall iron plate has
stopped the 7in. shot; but any strict analogies or
comparisons cannot be made out, because these de-
tails of the French experiments, which hasveiy
reachedentl
us from private sources, are not sufficiently
ample. We know that in these last Vincennes
trials the effect of two or three of the stringers in
the backing brought into resisting action simulta-
neously by the impact of the missile prevented pene-
tration even when fully charged, but we do not
lknow
the distance at which the gun was placed. Nr e also
know that when the shot got through the armour
where the plating was supported by only one stringer,.
the shot was turned aside and became jammed
in the backing. This would seem to indicate that
the number of iron laminae in the backing
might be
increased and the thickness of the wood planking
diminished, or, in other words,
that the more
frequent alternations of wood and iron planking
would be beneficial to resistance offered by the
Chalmers target. These particulars would also
seem to extend the proofs of the yalite of Mr,
Chalmers's system,