The
Imperial Japanese Navy's fleet of battleships had proven highly successful in
1905
, the last year of the Russo-Japanese war culminating in the destruction of the Russian Baltic Fleet at the Battle of Thushima. In the aftermath, the Japanese Empire immediately turned her focus to the two remaining rivals for imperial dominance in the Pacific Ocean: Britain and the United States. Satō Tetsutarō, a Japanese Navy admiral and military theorist, speculated that conflict would inevitably arise between Japan and at least one of their two main rivals. To that end, he called for the Japanese Navy to maintain a fleet with at least 70% as many capital ships as the US Navy. This ratio, Satō theorized, would enable the Imperial Japanese Navy to defeat the US Navy in a decisive battle in Japanese waters in any eventual conflict. To that end, the 1907 Imperial Defense Policy called for the construction of a battle fleet of eight modern battleships—20,000 long tons (20,000 t) each—and eight modern armored cruisers—18,000 long tons (18,000 t) each—to match the US Navy. This was the genesis of the Eight-Eight Fleet Program, the development of a cohesive battle line of sixteen capital ships.
, the last year of the Russo-Japanese war culminating in the destruction of the Russian Baltic Fleet at the Battle of Thushima. In the aftermath, the Japanese Empire immediately turned her focus to the two remaining rivals for imperial dominance in the Pacific Ocean: Britain and the United States. Satō Tetsutarō, a Japanese Navy admiral and military theorist, speculated that conflict would inevitably arise between Japan and at least one of their two main rivals. To that end, he called for the Japanese Navy to maintain a fleet with at least 70% as many capital ships as the US Navy. This ratio, Satō theorized, would enable the Imperial Japanese Navy to defeat the US Navy in a decisive battle in Japanese waters in any eventual conflict. To that end, the 1907 Imperial Defense Policy called for the construction of a battle fleet of eight modern battleships—20,000 long tons (20,000 t) each—and eight modern armored cruisers—18,000 long tons (18,000 t) each—to match the US Navy. This was the genesis of the Eight-Eight Fleet Program, the development of a cohesive battle line of sixteen capital ships.
The
launch of HMS Dreadnought in 1906 by the Royal
Navy "revolutionized capital ship design", and complicated Japan's plans.
Displacing 17,900 long tons (18,200 t) and armed with ten 12-inch (30 cm)
guns, Dreadnought rendered all existing battleships
obsolete by comparison. The
launch of the battlecruiser HMS Invincible the following year
was a further setback for Japan quest for parity. When Japan's two new Satsuma-class battleships and two Tsukuba-class armored cruisers, launched by 1911,
were outclassed by their British counterparts, the Eight-Eight Fleet Program
was restarted.
The
first battleships built for the Eight-Eight Fleet Program were the two dreadnoughts
of the Kawachi class, ordered in 1907 and laid
down in 1908.[15] In 1910, the Navy put
forward a request to the Diet of Japan (parliament) to secure funding for the
entirety of the program at once. Because
of economic constraints, thd proposal was cut first by the Navy Ministry to
seven battleships and three battlecruisers, then by the cabinet to what became
the Japanese Naval Emergency Expansion bill, authorizing the construction of
four battlecruisers (the Kongō class) and one battleship, later named Fusō.
Specification
 |
| Costruction of Fusō-class Battleship |
Main Battery
The primary
armament of the Fusō class was twelve 14-inch/45-caliber naval guns. Each gun was 648.4 inches
(16.47 m) in length, and weighed 86 metric tons (85 long
tons). The shells fired by the main guns varied throughout the lifespan of
the class. During World War I, Armour-Piercing Type 3 shells were used, each of
which weighed 1,400 pounds (640 kg). In 1925, APC Type 5 shells replaced
the previous ammunition, with APC No.6/Type 88 shells replacing these in
1928. During World War II, APC Type 91 shells were used. Each of these
shells weighed 1,485 pounds (674 kg), and was fired at an initial muzzle
velocity of 2,543 feet per second (2,790 km/h).
The main guns
of the Fusō class were mounted in six double turrets, each of
which weighed 615 long tons (625 t). Originally, the turrets had an
elevation capability of −5/+20 degrees. This configuration enabled
the Fusō battleships to outclass all of her contemporaries,
the most powerful of which were armed with ten 14-inch or eight 15-inch guns.
However, the location of the third and fourth turrets proved particularly
problematic to the design of the class. Mounted amidships along the
centreline of the ship (separated by a funnel), they had highly restricted arcs
of fire, and their positioning affected the internal layout of the
battleships. The shell rooms for each of the mountings had to be
positioned separately, which decreased the available space for other machinery
and hampered the armor configuration. The resultant ammunition magazines
amidships also necessitated a longer hull than Fusō's contemporaries.
The main
battery of the Fusō class underwent various modernizations
throughout the ships' careers. During the first reconstruction of both vessels,
the elevation of the main guns was increased to −5/+43 degrees, giving a
maximum firing range of 35,450 yards (20.14 mi; 32.42 km). The
recoil mechanism of the guns was also changed from a hydraulic to pneumatic
system, which allowed for a faster firing cycle of the main guns. The
purchase of French gun design patents in 1924 also enabled the 14-inch guns of
the Fusō class to be heavily modified and upgraded.
Secondary Armament
As built,
the Fusō class was fitted with a secondary armament of sixteen
152-millimetre (6.0 in)/50 caliber guns, four 76-millimetre
(3.0 in)/40 caliber guns, and six submerged 533-millimetre (21.0 in)
torpedo tubes. The 152 mm guns were mounted in single casemates along
the upper deck of the hull. Eight guns were mounted per side, and had a
horizontal angle of rotation of 130 degrees and a maximum vertical elevation of
+15 degrees. Each gun could fire a 45.36 kg (100.0 lb)
high-explosive projectile a maximum distance of 22,970 yards (13.05 mi;
21.00 km) at a rate of between four and six shots per minute. During
their reconstruction in the 1930s, the maximum elevation of the guns was increased
to +30 degrees, which increased the maximum range by approximately 900
metres. While the same guns mounted on other Japanese warships were
considered dual-purpose (antiship and antiaircraft), their restricted firing
arcs and training speed in casemates aboard Fusō and Yamashiro made
them unsuitable as antiaircraft weapons. The 76 mm high-angle guns
were in single mounts on both sides of the forward and aft superstructures,
both sides of the second funnel, as well as in two other (unspecified) locations. Each
of these guns had a maximum vertical elevation of 75 degrees, and could fire a
6 kg (13 lb) projectile at a vertical speed of 680 m/s
(1,500 mph; 2,400 km/h) with a maximum vertical ceiling of
7,500 m (24,600 ft).
The
configuration of the Fusō class's secondary armament changed
significantly over the course of the vessels' lives. During the main
modernization of the early 1930s, all eight 76 mm guns were removed and
replaced with eight 127 mm (5.0 in)/40 caliber Dual-Purpose (DP)
guns. These guns were fitted on both sides of the forward and aft
superstructures, and had the greatest variance in shell type among the guns
on Fusō. They could fire high-explosive antiaircraft shells, Shiki
Sankaidan ("Beehive") incendiary shells, illumination shells
and training shells. During reconstruction, the two foremost 152 mm
guns were also removed.
The light
antiaircraft armament of the Fusō class changed dramatically
during the years 1933–1944. During her first reconstruction, Fusō was
fitted with four 13.2 mm (0.52 in) machine-guns, while Yamashiro was
fitted with eight twin mounts of 25 mm (0.98 in) antiaircraft
guns. The 13.2 mm machine-guns were based on the French Hotchkiss
Machine Gun, and were considered to be a relatively poor design. The
25 mm was mounted on the Fusō class in single, double and
triple mounts. It was the standard Japanese light-antiaircraft gun during World
War II, but suffered from severe design shortcomings that rendered it a largely
ineffective weapon. The twin and triple mounts "lacked sufficient speed in
train or elevation; the gun sights were unable to handle fast targets; the gun
exhibited excessive vibration; the magazine was too small, and, finally, the
gun produced excessive muzzle blast". The configuration of the antiaircraft
guns varied significantly; By the end of their final reconstruction, the Fusō class
mounted eight twin mounts. In 1943, seventeen single and two twin-mounts were
added for a total of 37. In August 1944, both were fitted with another
twenty-three single, six twin and eight triple-mounts, for a total of 95
antiaircraft guns in their final configuration.
Armor
When
the Fusō class was completed, the ships' armor
was "typical for a pre-Jutland battleship". As built, the armor accounted for a
displacement of 8,588 long tons (8,726 t), approximately 29% of the
class's total displacement. The
main armored belt was 305 millimetres (12.0 in) thick, while the
underwater belt had a varying thickness of 102–152 mm (4.0–6.0 in). The horizontal armor was considered
light by World War I standards, with a thickness range from 32 to 51 mm (1.3 to
2.0 in). The turrets were more
heavily armored than those of theKongō class,
with a thickness of 305 mm (12.0 in) on the face, 203 mm
(8.0 in) on the sides, and 115 mm (4.5 in) on the roof. The barbettes of the turrets were
protected by 205 millimetres (8.1 in) of armor, while the casemates of the
152 mm guns were covered by 152 mm (6.0 in) of armor. The conning tower was very heavily
armored with variations of Krupp Cemented Armor up to 351 millimetres
(13.8 in) thick. Additionally,
the vessels contained 737 watertight compartments (574 underneath the armor
deck, 163 above) to preserve buoyancy in the event of battle damage.
During
their reconstruction in the 1930s, the armor of the Fusō class was substantially upgraded. The
horizontal armor was increased to a maximum thickness of 98 mm
(3.9 in), while an additional 17 mm (0.67 in) of armor plating
was added aft of the conning tower. Torpedo
bulges were also added, both to compensate for the increase in weight and to
add underwater protection, increasing the beam of the ship to by 4.43 metres
(14.5 ft). A longitudinal
bulkhead of 76 mm (3.0 in) was created to improve the underwater protection,
and extra plates were added to cover the original hull. 102 millimetres (4.0 in) of
plating were added to protect the ammunition magazines and machinery. This
brought the total armor tonnage up to 12,199 long tons (12,395 t), approximately 31% of the total
displacement of the Fusō class. Even after these improvements, the
armor was still incapable of withstanding 14-inch shells.
Propulsion
When
the Fusō-class battleships
were constructed, their machinery produced more power than other contemporary
battleships, whose design focused on armor at the expense of speed. During
trials, these power plants could produce 40,000 shaft horsepower (30,000 kW),
driving the ships through the water at a speed of 22.5 to 23.0 knots (25.9 to
26.5 mph; 41.7 to 42.6 km/h). The
power was generated by eight double-ended and sixteen single-ended
Miyahara-type boilers, all of which consumed a mixture of coal and oil. The boilers themselves were located in
four separate rooms. Both Fusō and Yamashiro were given two sets of Brown-Curtis turbines. Originally,
the Fusō-class battleships
had a stowage capacity for 4,000 long tons (4,100 t) of coal and 1,000
long tons (1,000 t) of oil, giving the battleships a 8,000-nautical-mile
(9,200 mi; 15,000 km) radius of operation. During their modernization, the
machinery of the Fusō class was replaced. The Miyahara
boilers were removed and the battleships fitted with six new Kampon oil-fired
boilers, while the main engine plant was replaced by four Kampon Turbines with
an increased output of 75,000 to 76,889 horsepower (56,000 to 57,336 kW). This enabled Fusō and Yamashiro to achieve a top speed of 25 knots
(29 mph; 46 km/h) with a radius of action of 11,800 nmi
(13,600 mi; 21,900 km).
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