One of the weakest parts of the Imperial Japanese Navy prior to World War II was that very little attention had been paid to protecting merchant ships against submarine attacks. Even after the war started, it wasn't until late 1943-early 1944 that a effort was made to increase the amount of resources devoted to ASW. By that time, it was a matter of too little, too late. No ahead-firing weapons equivalent to the Hedgehog or Squid were developed, although an ASW projectile for many naval guns and a simple mortar for merchant ships were introduced late in the war.

This low priority can be seen in the performance of the USA submarines vs. the Japanese ASW efforts. Japanese surface ships sank 17 USA submarines, aircraft sank eight and one was shared. In addition, one British submarine was sunk by aircraft and one by surface ships. By contrast, Allied Submarines sank 1,152 Japanese merchant ships of 4,861,317 gross tons, with the USA submarines accounting for about 98% of the totals. An equally impressive number of Japanese warships were sunk by submarines, with the giant aircraft carrier Shinano being the largest.

Japanese attacks were usually broken off too soon and the DC settings were too shallow.

"Blind Time" is the time between when a weapon is launched and when it reaches the target location. In addition, most early sonar systems lost the target submarine on close approach, usually requiring a "sprint" to reduce blind time. For depth charges, this meant that they were dropped or fired after the sonar contact was lost.

ASW Complement

In the early part of the Pacific War first-line destroyers carried almost no DCs at all while "Kaibokan" escorts carried 12 to 18. By the end of the war, most destroyers carried 30 DCs and escort vessels (kaibokan) carried about 120 including those stored below deck. Destroyers usually had only stern racks but escort vessels had six or eight depth charge throwers (DCT) and some Y guns.

Depth Charges

Type 88

Date Of Design 1928
Date In Service about 1930
Total Weight N/A
Explosive Charge 220 lbs. (100 kg) picric acid
Sink Rate / Terminal Velocity N/A
Settings 82 feet or 148 feet (25 or 45 m)

Used hydrostatic pistol. Obsolete and probably not in service by 1941.

Type 91 Model 1 Mod 1

Date Of Design 1931
Date In Service about 1935
Total Weight N/A
Explosive Charge 220 lbs. (100 kg) Type 88 charge
Sink Rate / Terminal Velocity N/A
Settings 82 feet or 164 feet (25 or 50 m)

Used hydrostatic pistol. Obsolete and probably not in service by 1941.

Type 95

Date Of Design 1935
Date In Service 1940
Total Weight 325 lbs. (160 kg)
Explosive Charge 220 lbs. (100 kg) Type 88 charge
Sink Rate / Terminal Velocity 6 fps (1.9 mps)
Settings 98 or 197 feet (30 or 60 m)
Later versions included a 295 foot (90 m) setting

This was the standard DC for the first half of World War II. Slow ships dropped it with a parachute which allowed them to escape the danger area. Unfortunately, it also allowed the submarine to escape. Parachute DC used only the shallower setting. Depth setting was controlled by varying the size of a water inlet, when the proper amount of water entered the charge would fire.

Type 2

Date Of Design 1942
Date In Service 1943
Total Weight N/A
Explosive Charge Mod 0: 231 lbs. (105 kg) Type 88
Mod 1: 357 lbs. (162 kg) Type 97 or 98
Mod 2: 243 lbs. (110 kg) Type 1 or 4
Sink Rate / Terminal Velocity 9.9 fps (3.0 mps)
Settings about 25 feet (7.6 m)

Almost a direct copy of British designs. Same sort of pistol as on the Type 95.

Depth Charge Racks

Designations and capabilities are not available at this time. Generally similar to USA versions.

Depth Charge Projectors

There were some broadside DCT and some Y guns but no ahead-throwing weapons such as Hedgehog. Possibly the most common was the Model 1934 which was first introduced in September 1934 and quickly became the standard DCT on Japanese ships. Known as the "Type Y launching device, depth charge twin launching device," this was a twin-arm Y launcher but could be used in single-side mode. Total weight of 1,500 lbs. (680 kg). When used with the Type 95 DC, range was 245 feet (75 m) for simultaneous firing and 345 feet (105 m) for single firing. Time of flight was 4.5 seconds for simultaneous firing and 5 seconds for single firing.

Anti-Submarine Projectiles

The Japanese developed anti-submarine projectiles for most naval guns between 3" (7.6 cm) and 6" (15.2 cm). These were Common Type 0 (1940) with a cylindrical head over the nose for the 6" (15.2 cm) and 5.5" (14 cm) guns and a flat-headed shell for the 5" (12.7 cm), 4.7" (12 cm) and 3" (7.6 cm) guns. These were introduced in 1943.

The larger guns had a muzzle velocity of about 820 fps (250 mps) and a range of 4,370-4,700 yards (4,000-4,300 m) at elevations of 40 degrees. The minimum range was 820-875 yards (750-800 m). The 3" (7.6 cm) projectile values were 3,500 yards (3,200 m) maximum and 765 yards (700 m) minimum.

ASW Mortars

A 15 cm (5.9") ASW mortar was developed for transports and merchant ships. This was in a cradle mounting allowing 360 degree traverse and had recoil and runout cylinders. The projectile weighed about 60 lbs. (27 kg) and could range out to a maximum of 4,500 yards (4,100 m).

The Navy 81 mm mortar was also carried by many escorts, firing standard projectiles.

Finally, a 15 cm (5.9") rocket propelled DC with a range of 3,280 yards (3,000 meters) was developed in April 1945 but this saw no active service.

Sources

Data from:

  • "Naval Weapons of World War Two" by John Campbell
  • "US Naval Weapons" and "The Naval Institute Guide to World Naval Weapon Systems 1991/92" both by Norman Friedman
  • "Japanese 'Kaibokan' Escorts" article by Hans Lengerer in "Warships Volume VIII"
  • "US Warships of World War II" by Paul H. Silverstone