_Turrets and Cupolas._--The difference between a turret and a cupola is
that the former is cylindrical with a flat or nearly flat top and
presents a vertical target; while the latter is a flattened dome, the
vertical supports of which are entirely concealed. The turret appears to
be little used. The object of both forms is at once to give an all-round
arc of fire to the guns and to allow of the weak point of the structure,
the port-hole and muzzle of the gun, being turned away from the enemy in
the intervals of firing. Both usually emerge from a mass of concrete,
which is strengthened round the opening by a collar of chilled cast iron
about 12 to 15 in. thick.
Cupolas.
There are four types of cupolas, viz. (a) Disappearing, (b)
Oscillating, (c) Central pivot, (d) On roller rings.
(a) Disappearing cupolas are used chiefly for small quick-firing guns,
on account of the expense of the various systems. They can be used for
medium guns. The details of the best foreign systems are secret. (b)
The oscillating turret is a Mougin type, in which the turret is
supported in the centre by a knife-edge on which it can swing. The
oscillation is controlled by powerful springs. The effect of it is
that after firing, the front of the cupola with the port-hole swings
downwards under cover, and is held there until the gun is ready to
fire again. (c) Schumann's centre pivot is understood to be approved
in Germany. It has been adopted in Rumania and Belgium for howitzer
cupolas. It is only suitable for a single piece; d is strong and
steady--the best cupola for coast batteries; c and d are best for
rapid fire because they can be loaded without lowering. They are
suited for long guns.
The following types are illustrated as being generally representative
of the different classes of cupola.
[Illustration: FIG. 56.--Cupola for 6-in. gun (Friedr. Krupp A.G.).]
Fig. 56 is a section of Messrs Krupp's typical cupola for one 6-in.
gun. The shield is of nickel steel, the collar of cast steel. A small
space is left between the cupola and its collar to prevent the
possibility of the shield jamming after being damaged. The guns are
muzzle-pivoting and thickened out near the muzzle by the addition of a
ring, so as to close the port as much as possible. The recoil is
controlled within narrow limits both to economize space and to prevent
the smoke from the muzzle from getting into the cupola. To facilitate
the elevation and depression of the gun (with muzzle pivotings the
breech has of course to be moved through a much larger arc than with
ordinary mountings) it is balanced by a counterweight. The cupola
rests on a roller ring and is traversed by a winch. It can be turned
through a complete circle in about one minute.
[Illustration: From Leithner's _Bestandige Befestigung_.