| Notes:
1) These mountings varied in detail from
class to class and even within a class but many features were the same.
They were operated with very noisy electric motor driven oil hydraulic
pumps located in the revolving structure. Damage to rubber insulated
wiring by oil leaks was a common complaint. Run out was by compressed
air. Training was by a 50 hp electric motor which drove hydraulic
gear. Elevation was by rack and pinion. A 75 hp motor drove
two hydraulic pumps which provided power to a common ring. This ring
supplied hydraulic actuators for elevating the guns, ramming and the ammunition
hoists. Fuzes were set on the loading tray. D mountings had
236 inch (6 m) rangefinders.
2) None of the mountings used on carriers
could fire cross-deck.
3) Model "B," "C" and "D" mountings had
thin steel sheeting along the top and sides to provide a 10 cm (3.9") air
space around the turrets. This provided shading for tropical service.
4) The "B" Model mountings used on the
carriers Akagi and Kaga were actually designed sometime later than the
"C" and "D" Models. "B" Model mountings were nearly the same as the
Model "E" used on the Takao class heavy cruisers, the difference being
that the "B" Model used the 20 cm (7.9") Type 3 No. 1 guns while the "E"
Model used the
20 cm (8") Type 3 No. 2 guns.
Like the "E" Model mounts, the "B" Model mounts had two hoists per gun,
while
the other Models had one. The second hoist was intended to support
higher angle (anti-aircraft) firing by making it easier to change ammunition
types, but they resulted in a larger turret trunk, a larger lower chamber,
increased turret weight and added crewmen. As loading was performed
at +5 degrees and the training and elevation speeds were low, the reality
was that these mounts were of little use for anti-aircraft defense.
The maximum elevation of the "B" Model was +70 degrees, but the elevating
and recoil mechanisms proved to be fragile and it was found that +55 degrees
was the maximum practical elevation. These twin mountings were removed
from Akagi and Kaga during their reconstruction in the 1930s and after
that time they carried only single 20 cm (7.9") guns in casemate mountings.
5) The twin mount gun axes were 74.8 in
(190 cm) apart.
6) At the Kosaku Ariga (Jarek) website
listed below, there are many pictures of a Japanese-built 20 cm (7.9")
mounting used on the Thailand Coastal Defense ship HTMS Dhonburi.
At that website, this mounting is variously described as a Myoko-class
style mounting or as a mounting removed from the carrier Kaga. From
my examination of these photographs and others, I believe that only the
first of these statements is correct. The turret used on Dhonburi
shows the sloped-roof and super-imposed rangefinder typical of earlier
20 cm (7.9") No. 1 mountings such as those used on the Myoko class.
The "B" Model mountings used on Kaga (and the "E" Model mountings used
on later cruisers) had flat roofs and the rangefinder was partially enclosed
within the mounting. I believe that the guns in this Thailand mounting
are the 20 cm (7.9") Type 3 No. 1 guns, as the chase shows a tapering after
the "C" tube that does not appear in photographs of the 20 cm (8") Type
3 No. 2 guns used on Japanese heavy cruisers during World War II.
As a guess, the guns used for Dhonburi could have been among those removed
from Japanese cruisers when the latter was upgraded to the larger 20 cm
(8") Type 3 No. 2 guns. |
