Japanese Interwar Antiaircraft Guns (1916-1939)
The World War II ships of the Imperial Japanese Navy are often criticized for their inadequate air defense armament. Now, this critique is somewhat arguable for a variety of reasons, but this post is instead going to look at the more neglected subject of how Japanese air defense guns reached the point they were at when the war began. Popular military history loses a lot of context by focusing on wars rather than peacetime developments, and nowhere is that more true than in the subject of aircraft World War II. It must always be remembered that aircraft evolved rapidly over the interwar period and much of what they accomplished during World War II would have been impossible just a few years earlier.
Contrary to popular belief, the major navies of the world were quite forward-looking when it came to aircraft, and this includes the matter of air defense. The Royal Navy introduced its first dedicated antiaircraft gun (the 12 pounder QF HA Mk 1) in 1913, and the Imperial German Navy and United States Navy both followed suit the very next year with the 88mm Flak L/45 and the 3"/50 Mk 10. The Imperial Japanese Navy lagged somewhat behind the big three, and did not field its first antiaircraft gun until 1916. However, this is not exactly surprising as the 1914 Imperial Japanese Navy was still quite small and did not yet possess a single dreadnought battleship.
The 1916 gun was the 3"/40 3rd Year Type and was fairly comparable to the British, German, and American guns. Emplaced in unshielded single mounts, it could elevate to 75º and was manually operated with elevation and traverse rates of around 10º per second. It fired fixed ammunition with a 12.5 pound projectile at a muzzle velocity of around 2200 feet per second and had a rate of up to 20 rounds per minute (though without ammunition hoists this could only be maintained for short periods before the ready ammunition was expended).
While battleships were all quickly armed with two to four of these guns, other ships made do with nothing more than small numbers of the 6.5mm 3rd Year Type machine gun - a modified Hotchkiss M1914 produced under license and firing the standard Japanese rifle cartridge. These weapons were air-cooled and fed by 30 round rigid metal belts. While this feed method is somewhat odd by today’s standards, a two man team could maintain nearly uninterrupted fire and the M1914 and its derivatives were quite well regarded and widely exported. Muzzle velocity was 2400 feet per second and the cyclic rate of fire was around 450 rounds per minute.
Although this armament was paltry by World War II standards, it was in line with what other navies were then adopting and not entirely inadequate given the threat. After all, at that time there were no real tactics or equipment for attacking ships from the air and the weapons were mostly needed for harassing reconnaissance aircraft and zeppelins at medium altitude. However, this was rapidly changing and several nations experimented with torpedo bombers during World War I, and 1921 marked the sinking of the former German battleship Ostfriesland by United States Army heavy bombers. Although in hindsight the former was the far greater threat, it appears that it was the latter that captured the imagination and navies around the world continued to focus on large caliber guns for fending off high altitude aircraft.
Over the course of the 1920’s, the 3"/40 remained the standard Japanese antiaircraft weapon and slowly proliferated through the fleet. Battleships generally received six or seven guns while cruisers were armed with just one or two. The new Furutaka-class heavy cruisers and the carrier Hosho both had four 3/"/40 guns. The 6.5mm machine guns were also gradually replaced with imported .303 Lewis guns designated the 7.7mm RU Type. The domestically-produced version of this gun was later designed the 7.7mm Type 92, which makes it easily confused with the Imperial Japanese Army's entirely unrelated Hotchkiss-derived 7.7mm Type 92 machine guns. The Navy gun was fed by a 47 round pan magazine with a cyclic rate of fire of around 600 rounds per minute and a muzzle velocity of 2500 feet per second, making it a real improvement over the older 6.5mm machine guns.
During the final years of the 1920’s two new large caliber weapons appeared - the 4.7”/45 10th Year Type and the 5”/50 3rd Year Type. The 4.7”/45 was a dedicated antiaircraft gun that superseded the 3”/40 on carriers and heavy cruisers, beginning in 1927 with Akagi, Kaga, and the Aoba-class. The carriers received six twin mounts while the cruisers were armed with four single mounts. The 4.7”/45 was far more powerful than the 3”/40, firing a 45 pound shell at a muzzle velocity of 2700 fps. This meant both a larger lethal radius and an increase in ceiling from 24,000 feet to 33,000 feet - both vital improvements to counter faster and higher-flying aircraft. However, in other ways the weapon was little improved over the 3”/40, as it was still a manually operated gun with an elevation of 75º. Further, the much heavier fixed ammunition mean that the rate of fire fell dramatically to around 10 rounds per minute.
In contrast the 5”/50 was something new - a dual-purpose weapon intended for both antiship and antiaircraft use. Entering service in 1928 on the Fubuki-class destroyers, this marked the first time a Japanese destroyer was armed with more than machine guns for air defense. In some ways the 5”/50 was actually a superior gun to the 4.7”/45, as it fired a 51 pound shell at a muzzle velocity of 3000 fps while maintaining the same 10 rounds per minute rate of fire. However, unlike the 4.7”/45, the 5”/50 was primarily an antiship weapon and it had a maximum elevation of just 55º (although this was increased to 75º on some later mounts). Further, the 5”/50 used separate bagged charges and could only be loaded when at an elevation of 10º or less, drastically reducing rate of fire against high altitude targets and forcing the gun crew to aim between every shot.
By the end of the 1920’s, the standard Japanese antiaircraft armament was as follows:
Battleships: 4-7x 3”/40
Fleet Carriers: 12x 4.7”/45
Heavy Cruisers: 4-6x 4.7”/45
Light Cruisers: 1-2x 3”/40
Destroyers: 6x 5"/50
In 1932, the 5”/40 Type 89 antiaircraft gun was introduced to replace both the 4.7”/45 and the 3”/40 on all major warships. Firing fixed ammunition with a 51 pound shell at a rate of up to 14 rounds per minute with a muzzle velocity of 2400 feet per second and a ceiling of 31,000 feet, these mounts were very comparable to the famous American 5"/38. Significant advantages over the older Japanese antiaircraft guns included a maximum elevation of 90º and fully enclosed turrets with ammunition hoists and hydraulic traverse and elevation. Battleships and heavy cruisers were armed with four twin mounts while fleet carriers had six or eight.
Also in 1932, the Japanese also began fielding the Hotchkiss 13mm Type 93 heavy machine gun to replace their 6.5mm and 7.7mm machine guns. This new weapon came in single, twin, and quad mounts, all of which had geared traverse and elevation controlled by a gunner instead of the flexible mounts of the older weapons. The quad mounts were relatively rare, but the twin and single mounts generally replaced the rifle-caliber machine guns on a one-for-one basis. The 13mm gun was fed from 30 round magazines with a cyclic rate of fire of around 450 rounds per minute and a muzzle velocity of 2600 feet per second. While this rate of fire was lower than that of the 7.7mm guns, the heavier bullet was becoming increasingly necessary to knock down the more durable aircraft of the period.
However, the 13mm gun was only an interim weapon the larger Hotchkiss 25mm Type 96 was introduced in 1935. This gun had a cyclic rate of fire of around 250 rounds per minute and was fed from 15 round magazines with a muzzle velocity of 2900 feet per second. While the 25mm was later available in single, twin, and triple mounts, only the twin mount appears to have been used during the 1930’s and it generally replaced 13mm mounts on a one for one basis. When in a twin mount it was served by a crew of seven, with three men responsible for aiming and four for loading (the magazines would need to be changed every 4 seconds).
By 1939, the standard Japanese antiaircraft armament was as follows:
Battleships: 8x 5”/40, 20x 25mm
Fleet Carriers: 12x 5”/40, 22-28x 25mm
Heavy Cruisers: 8x 5”/40, 12x 25mm (shortages meant many had 8x 25mm and 4x 13mm)
Light Cruisers: 4x 25mm, 4x 13mm
Destroyers: 5-6x 5”/50, 4x 25mm
Thus, on the brink of World War II, the Imperial Japanese Navy had a rational two layer system of air defense guns. The 5"/40 was a solid weapon and comparable to the heavy antiaircraft guns of any other navy, while the 25mm cannon was powerful and reliable. Even in the number of antiaircraft guns carried the Japanese ships were better off than those of most other nations. The only real deficiency was the continued use of the 5"/50 on destroyers, sacrificing antiaircraft effectiveness for a more potent antiship weapon, but even this was an understandable choice at the time. While the Imperial Japanese Navy failed to maintain this edge during wartime, it still deserves greater respect for its pre-war air defense planning than it commonly receives.
Contrary to popular belief, the major navies of the world were quite forward-looking when it came to aircraft, and this includes the matter of air defense. The Royal Navy introduced its first dedicated antiaircraft gun (the 12 pounder QF HA Mk 1) in 1913, and the Imperial German Navy and United States Navy both followed suit the very next year with the 88mm Flak L/45 and the 3"/50 Mk 10. The Imperial Japanese Navy lagged somewhat behind the big three, and did not field its first antiaircraft gun until 1916. However, this is not exactly surprising as the 1914 Imperial Japanese Navy was still quite small and did not yet possess a single dreadnought battleship.
The 1916 gun was the 3"/40 3rd Year Type and was fairly comparable to the British, German, and American guns. Emplaced in unshielded single mounts, it could elevate to 75º and was manually operated with elevation and traverse rates of around 10º per second. It fired fixed ammunition with a 12.5 pound projectile at a muzzle velocity of around 2200 feet per second and had a rate of up to 20 rounds per minute (though without ammunition hoists this could only be maintained for short periods before the ready ammunition was expended).
While battleships were all quickly armed with two to four of these guns, other ships made do with nothing more than small numbers of the 6.5mm 3rd Year Type machine gun - a modified Hotchkiss M1914 produced under license and firing the standard Japanese rifle cartridge. These weapons were air-cooled and fed by 30 round rigid metal belts. While this feed method is somewhat odd by today’s standards, a two man team could maintain nearly uninterrupted fire and the M1914 and its derivatives were quite well regarded and widely exported. Muzzle velocity was 2400 feet per second and the cyclic rate of fire was around 450 rounds per minute.
Although this armament was paltry by World War II standards, it was in line with what other navies were then adopting and not entirely inadequate given the threat. After all, at that time there were no real tactics or equipment for attacking ships from the air and the weapons were mostly needed for harassing reconnaissance aircraft and zeppelins at medium altitude. However, this was rapidly changing and several nations experimented with torpedo bombers during World War I, and 1921 marked the sinking of the former German battleship Ostfriesland by United States Army heavy bombers. Although in hindsight the former was the far greater threat, it appears that it was the latter that captured the imagination and navies around the world continued to focus on large caliber guns for fending off high altitude aircraft.
Over the course of the 1920’s, the 3"/40 remained the standard Japanese antiaircraft weapon and slowly proliferated through the fleet. Battleships generally received six or seven guns while cruisers were armed with just one or two. The new Furutaka-class heavy cruisers and the carrier Hosho both had four 3/"/40 guns. The 6.5mm machine guns were also gradually replaced with imported .303 Lewis guns designated the 7.7mm RU Type. The domestically-produced version of this gun was later designed the 7.7mm Type 92, which makes it easily confused with the Imperial Japanese Army's entirely unrelated Hotchkiss-derived 7.7mm Type 92 machine guns. The Navy gun was fed by a 47 round pan magazine with a cyclic rate of fire of around 600 rounds per minute and a muzzle velocity of 2500 feet per second, making it a real improvement over the older 6.5mm machine guns.
During the final years of the 1920’s two new large caliber weapons appeared - the 4.7”/45 10th Year Type and the 5”/50 3rd Year Type. The 4.7”/45 was a dedicated antiaircraft gun that superseded the 3”/40 on carriers and heavy cruisers, beginning in 1927 with Akagi, Kaga, and the Aoba-class. The carriers received six twin mounts while the cruisers were armed with four single mounts. The 4.7”/45 was far more powerful than the 3”/40, firing a 45 pound shell at a muzzle velocity of 2700 fps. This meant both a larger lethal radius and an increase in ceiling from 24,000 feet to 33,000 feet - both vital improvements to counter faster and higher-flying aircraft. However, in other ways the weapon was little improved over the 3”/40, as it was still a manually operated gun with an elevation of 75º. Further, the much heavier fixed ammunition mean that the rate of fire fell dramatically to around 10 rounds per minute.
In contrast the 5”/50 was something new - a dual-purpose weapon intended for both antiship and antiaircraft use. Entering service in 1928 on the Fubuki-class destroyers, this marked the first time a Japanese destroyer was armed with more than machine guns for air defense. In some ways the 5”/50 was actually a superior gun to the 4.7”/45, as it fired a 51 pound shell at a muzzle velocity of 3000 fps while maintaining the same 10 rounds per minute rate of fire. However, unlike the 4.7”/45, the 5”/50 was primarily an antiship weapon and it had a maximum elevation of just 55º (although this was increased to 75º on some later mounts). Further, the 5”/50 used separate bagged charges and could only be loaded when at an elevation of 10º or less, drastically reducing rate of fire against high altitude targets and forcing the gun crew to aim between every shot.
By the end of the 1920’s, the standard Japanese antiaircraft armament was as follows:
Battleships: 4-7x 3”/40
Fleet Carriers: 12x 4.7”/45
Heavy Cruisers: 4-6x 4.7”/45
Light Cruisers: 1-2x 3”/40
Destroyers: 6x 5"/50
In 1932, the 5”/40 Type 89 antiaircraft gun was introduced to replace both the 4.7”/45 and the 3”/40 on all major warships. Firing fixed ammunition with a 51 pound shell at a rate of up to 14 rounds per minute with a muzzle velocity of 2400 feet per second and a ceiling of 31,000 feet, these mounts were very comparable to the famous American 5"/38. Significant advantages over the older Japanese antiaircraft guns included a maximum elevation of 90º and fully enclosed turrets with ammunition hoists and hydraulic traverse and elevation. Battleships and heavy cruisers were armed with four twin mounts while fleet carriers had six or eight.
Also in 1932, the Japanese also began fielding the Hotchkiss 13mm Type 93 heavy machine gun to replace their 6.5mm and 7.7mm machine guns. This new weapon came in single, twin, and quad mounts, all of which had geared traverse and elevation controlled by a gunner instead of the flexible mounts of the older weapons. The quad mounts were relatively rare, but the twin and single mounts generally replaced the rifle-caliber machine guns on a one-for-one basis. The 13mm gun was fed from 30 round magazines with a cyclic rate of fire of around 450 rounds per minute and a muzzle velocity of 2600 feet per second. While this rate of fire was lower than that of the 7.7mm guns, the heavier bullet was becoming increasingly necessary to knock down the more durable aircraft of the period.
However, the 13mm gun was only an interim weapon the larger Hotchkiss 25mm Type 96 was introduced in 1935. This gun had a cyclic rate of fire of around 250 rounds per minute and was fed from 15 round magazines with a muzzle velocity of 2900 feet per second. While the 25mm was later available in single, twin, and triple mounts, only the twin mount appears to have been used during the 1930’s and it generally replaced 13mm mounts on a one for one basis. When in a twin mount it was served by a crew of seven, with three men responsible for aiming and four for loading (the magazines would need to be changed every 4 seconds).
By 1939, the standard Japanese antiaircraft armament was as follows:
Battleships: 8x 5”/40, 20x 25mm
Fleet Carriers: 12x 5”/40, 22-28x 25mm
Heavy Cruisers: 8x 5”/40, 12x 25mm (shortages meant many had 8x 25mm and 4x 13mm)
Light Cruisers: 4x 25mm, 4x 13mm
Destroyers: 5-6x 5”/50, 4x 25mm
Thus, on the brink of World War II, the Imperial Japanese Navy had a rational two layer system of air defense guns. The 5"/40 was a solid weapon and comparable to the heavy antiaircraft guns of any other navy, while the 25mm cannon was powerful and reliable. Even in the number of antiaircraft guns carried the Japanese ships were better off than those of most other nations. The only real deficiency was the continued use of the 5"/50 on destroyers, sacrificing antiaircraft effectiveness for a more potent antiship weapon, but even this was an understandable choice at the time. While the Imperial Japanese Navy failed to maintain this edge during wartime, it still deserves greater respect for its pre-war air defense planning than it commonly receives.
