The twelve 45-calibre 14-inch guns of the Fusō class were mounted in six twin-gun turrets, numbered from front to rear, each of which weighed 615 long tons (625 t).
The turrets had an elevation capability of −5/+20 degrees.
They were arranged in an uncommon 2-1-1-2 style with superfiring pairs of turrets fore and aft; the middle turrets were not superfiring, and had a funnel between them.
The decision to use six twin turrets rather than four triple turrets greatly affected the entire design of the class because the two extra turrets required a longer ship and increased the amount of armor required to protect the ship.
The location of the third and fourth turrets proved particularly problematic to the design of the class because the amidships turrets were not superfiring as in the subsequent Ise-class battleships.
This further increased the length of the ships because the barrels of the upper turret did not protrude over the lower turret, requiring more space than a pair of superfiring turrets.
Mounted amidships along the centerline of the ship, they had restricted arcs of fire, and their position forced the boiler rooms to be placed in less than ideal locations.
Another complication was the need to fit extra insulation and air conditioning in the magazines of the amidships turrets to protect them from the heat generated in the adjacent boiler rooms.
Originally both amidship gun turrets faced to the rear, but Fusō's turret No.
3 was moved to face forward during her reconstruction in order to accommodate additional platforms around her funnel.

The main battery of the Fusō class underwent multiple 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 (32,420 m).
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.

By World War II, the guns used Type 91 armor-piercing, capped shells.
Each of these shells weighed 673.5 kilograms (1,485 lb) and had a muzzle velocity of 775 meters per second (2,540 ft/s).
They had a maximum range of 27,800 meters (30,400 yd) at +30 degrees of elevation and 35,450 meters (38,770 yd) at +43 degrees after modernization.
Also available was a 625-kilogram (1,378 lb) high-explosive shell that had a muzzle velocity of 805 meters per second (2,640 ft/s).
A special Type 3 Sankaidan incendiary shrapnel shell was developed in the 1930s for anti-aircraft use.

As built, the Fusō class was fitted with a secondary armament of sixteen 50-caliber six-inch guns mounted in single casemates along the sides of the hull at the level of the upper deck.
Eight guns were mounted per side, and each had an arc of fire of 130 degrees and a maximum elevation of +15 degrees.
Each gun could fire a 45.36-kilogram (100.0 lb) high-explosive projectile a maximum distance of 22,970 yards (21,000 m) 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 their maximum range by approximately 900 metres (980 yd).

The ships also mounted five or six 40-caliber 76 mm anti-aircraft (AA) guns.
The 76-millimetre (3 in) high-angle guns were in single mounts on both sides of the forward superstructure, both sides of the second funnel, and each side of the aft superstructure (Fusō lacked the starboard side aft gun).
Each of these guns had a maximum elevation of +75 degrees, and could fire a 6 kg (13 lb) projectile with a muzzle velocity of 680 m/s (2,200 ft/s) to a maximum height of 7,500 metres (24,600 ft).
Both ships were equipped with six submerged 533-millimetre (21.0 in) torpedo tubes, three on each broadside.

The Fusō class's secondary armament changed significantly over time.
During the modernizations of the 1930s, all of the 76 mm guns were replaced with eight 40-caliber 127 mm (5.0 in) dual-purpose guns.
These guns were fitted on both sides of the fore and aft superstructures in
The twelve 45-calibre 14-inch guns of the Fusō class were mounted in six twin-gun turrets, numbered from front to rear, each of which weighed 615 long tons (625 t). The turrets had an elevation capability of −5/+20 degrees. They were arranged in an uncommon 2-1-1-2 style with superfiring pairs of turrets fore and aft; the middle turrets were not superfiring, and had a funnel between them. The decision to use six twin turrets rather than four triple turrets greatly affected the entire design of the class because the two extra turrets required a longer ship and increased the amount of armor required to protect the ship. The location of the third and fourth turrets proved particularly problematic to the design of the class because the amidships turrets were not superfiring as in the subsequent Ise-class battleships. This further increased the length of the ships because the barrels of the upper turret did not protrude over the lower turret, requiring more space than a pair of superfiring turrets. Mounted amidships along the centerline of the ship, they had restricted arcs of fire, and their position forced the boiler rooms to be placed in less than ideal locations. Another complication was the need to fit extra insulation and air conditioning in the magazines of the amidships turrets to protect them from the heat generated in the adjacent boiler rooms. Originally both amidship gun turrets faced to the rear, but Fusō's turret No. 3 was moved to face forward during her reconstruction in order to accommodate additional platforms around her funnel.
The main battery of the Fusō class underwent multiple 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 (32,420 m). 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.
By World War II, the guns used Type 91 armor-piercing, capped shells. Each of these shells weighed 673.5 kilograms (1,485 lb) and had a muzzle velocity of 775 meters per second (2,540 ft/s). They had a maximum range of 27,800 meters (30,400 yd) at +30 degrees of elevation and 35,450 meters (38,770 yd) at +43 degrees after modernization. Also available was a 625-kilogram (1,378 lb) high-explosive shell that had a muzzle velocity of 805 meters per second (2,640 ft/s). A special Type 3 Sankaidan incendiary shrapnel shell was developed in the 1930s for anti-aircraft use.
As built, the Fusō class was fitted with a secondary armament of sixteen 50-caliber six-inch guns mounted in single casemates along the sides of the hull at the level of the upper deck. Eight guns were mounted per side, and each had an arc of fire of 130 degrees and a maximum elevation of +15 degrees. Each gun could fire a 45.36-kilogram (100.0 lb) high-explosive projectile a maximum distance of 22,970 yards (21,000 m) 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 their maximum range by approximately 900 metres (980 yd).
The ships also mounted five or six 40-caliber 76 mm anti-aircraft (AA) guns. The 76-millimetre (3 in) high-angle guns were in single mounts on both sides of the forward superstructure, both sides of the second funnel, and each side of the aft superstructure (Fusō lacked the starboard side aft gun). Each of these guns had a maximum elevation of +75 degrees, and could fire a 6 kg (13 lb) projectile with a muzzle velocity of 680 m/s (2,200 ft/s) to a maximum height of 7,500 metres (24,600 ft). Both ships were equipped with six submerged 533-millimetre (21.0 in) torpedo tubes, three on each broadside.
The Fusō class's secondary armament changed significantly over time. During the modernizations of the 1930s, all of the 76 mm guns were replaced with eight 40-caliber 127 mm (5.0 in) dual-purpose guns. These guns were fitted on both sides of the fore and aft superstructures in
Fusō-class battleship