| 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. C model had the
shell rooms and magazines on the same level while the D mountings had the
shell rooms below the magazines. D mountings had 236 inch (6 m) rangefinders.
2) None of the mountings used on carriers
could fire cross-deck.
3) Mountings had only splinter protection,
25.4 mm (1") of NVNC steel plates on all sides except the bottom, which
was protected by 19 mm (0.75"). 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) The Kosaku Ariga (Jarek) website has
apparently disappeared. At that website, there were many pictures
of a Japanese-built 20 cm (7.9") twin mounting used on the Thailand Coastal
Defense ship HTMS Dhonburi. Jarek sent these to me some years ago
for review and I have now added these pictures on the Additional Photographs
page above. On his website, Jarek described this mounting as a Myôkô-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 same sloped-roof and super-imposed rangefinder typical of earlier
20 cm (7.9") No. 1 mountings such as those used on the Myôkô
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 were upgraded to the larger 20 cm
(8") Type 3 No. 2 guns. |
