03-05-2007, 03:05 PM
I have been researching WWII Japanese Submarine operations; ....and while this topic will be of limited use to players of SH4 (due to the lack of Enemy Sub AI), I found it to be a really interesting topic: ....And while proper treatment of the subject really requires a book, I though that the "rank and file" here might find a brief summary to be an interesting read!


The West Coast of the U.S. became an active Japanese patrol zone from December of 1941, and continued to be so all through 1942. The strategy behind these missions and the tactics employed differed considerably from normal U-Boat tactics. The Japanese planners wanted to keep the U.S. "off balance" after the attack on Pearl Harbor; .....and they correctly deduced that a West Coast submarine threat would tie up a considerable number of patrol vessels and aircraft that were desperately needed elsewhere.

In other submarine services, a patrol off a hostile shore meant stealth: ....In the case of these Japanese West Coast Patrols, the subs were told to be noticed!! ...As a consequence, the Japanese I-Boats were dispatched on some of the most interesting submarine missions on record.

The "B Class" was the most numerous of the many different Japanese sub classes. There were three sub-classes; the B1, B2, and B3. They were all similar in size, but the B3 had a lower top speed, in exchange for a longer range.

Nine "B Class" boats patrolled the West Coast, covering an area that stretched from the Aleutians to San Diego: ......And these boats were well equipped for the job!


In the "Weapons Department" these boats were actually better equipped than the U.S. Gato Class. Many "experts" will disagree here, pointing out that the Gatos had four more tubes and carried nine more torpedoes; .....but the "real world reality" is that this numeric advantage is more than offset by the fact that the Japanese had the best torpedo in the world, and the U.S. had the worst!

The 140mm/50 (5.5") deck gun was also an excellent piece. Firing an 83 pound projectile at a muzzle velocity of 2800 feet per second (854 mps), it had a maximum range of 21,600 yards (19,750 meters). In the Pacific, the only submarine mounted gun that out-performed it was the 6"/53s that were mounted by the Narwhal Class boats.

The really remarkable piece of equipment that set these boats apart was the light float plane they were equipped with. The aircraft was a Yokosuka E14Y (Allied codename "Glen"). It was designed as a "takedown" aircraft, with removable wings and pontoons, which allowed it to be stored in a relatively small waterproof hangar on the forward deck. It was launched with the aid of a compressed air catapult. (A permanent installation on the forward deck.)


This little guy was really perfect for the application. It made up for it's relatively low top speed of 130 miles per hour with short take-off and landing capabilities, and it could either carry an observer or a 60 kg bomb load.

The "Glen" launched from the I-25 holds the distinction of being the only aircraft in history to have dropped bombs on the Continental United States! (.....At least the only confirmed bombing.)

The I-25 was very active off the West Coast of the U.S.: ....Her "Glen" conducted two bombing raids against the Pacific Northwest, and at least one recon flight on 20 June 1942, that resulted in the I-25's deck gun attack against the S.S. FORT CAMOSUN at Kodiak Alaska.

On 21 June, the I-25 fired seventeen 140mm rounds at Fort Stevens, Oregon. The resulting damage was taken very seriously by base personnel; ....as the backstop on the camp's baseball field was totally destroyed.

In September of 1942, the I-25 twice launched her "Glen" on bombing missions intended to start forest fires in the Oregon Forests. The incendiary bomb attacks were foiled by wet weather, and remarkably fast work by U.S. Forestry Service personnel.

Later, in October, the I-25 sank the tankers S.S. CAMDEN and S.S. LARRY DOHENY off the Oregon coast.


A sister ship to the I-25, the I-26, was also busy. She is credited with sinking the first U.S. merchant of the war when she sank the S.S. CYNTHIA OLSON, bound for Honolulu, from Tacoma Washington. Later, in June of 1942 she sank the S.S. COAST TRADER off the coast of Washington State. In the same month, she also shelled the Lighthouse and radio direction finding station at Estevan Point.

Another sister ship, the I-17, used her deck gun to shell an oil pumping station near Santa Barbara, California. Several days later, an incident occurred that has become known as the "Los Angles Air Raid".


This event proved the worth of the Japanese psychological efforts on the West Coast. The inexperienced AA crews around Los Angles lit up the sky with AA fire, while the local Army Air Corps prayed that they wouldn't be sent up: .....as they had no desire to be killed by "friendly fire"! (God only knows how many fires and how much damage occurred when all those AA shells fell back to earth!!!)

Officially, no evidence of an enemy aircraft was found, but after reading the accounts of the incident, and knowing that the I-17 was in the area, I strongly suspect that the cause of the panic was the "Glen" from I-17.

Today, in the best tradition of Southern California, many locals believe that it was a UFO event! (You really have to know California to understand how typical this is!)



These monsters were the largest submarines in the world at the time, and remained so until the advent of the modern nuclear "Boomer". Not only were they 60% larger than the Narwhal Class U.S. boats but they still hold the all-time range record for a diesel-electric sub: ....An astonishing 37,500 nautical miles!!! These boats could cruise 1 times around the World without refueling!

The most distinguishing feature of the Sen-Kotu Class (also known as the I-400 Class) is the 115 foot long waterproof hangar built into the superstructure. This hangar houses THREE Aichi M6A1 Seiran floatplanes.


These planes were some of the more remarkable aircraft seen in WWII! In spite of the fact that they were designed with the necessary "take-down" features required for submarine service, they offered the kind of performance generally seen only in Carrier Aircraft.

They had a top speed of 295 miles per hour, a range of 650 nautical miles; ....and could deliver up to an 800 kg bomb load, or one aerial torpedo. (The same aerial torpedo that was such a "smash hit" at Pearl Harbor!!)

The whole concept was amazingly well engineered. Since the aircraft had to be partially disassembled for storage in the hangar, the mating surfaces of the various parts were coated with luminescent paint, to facilitate assembly in the dark. The procedure worked so well that a trained four man crew could have an aircraft ready for flight in seven minutes. Even more impressive was the fact that it only took 45 minutes from the time the submarine surfaced for all aircraft to be airborne!!

These boats and their aircraft were not simply an interesting theoretical exercise for the Japanese Planners: ......They were designed specifically for attacking the Panama Canal, and the shipping in the area.

Now, as any Kaleun reading this can appreciate, The Panama Canal is probably the sweetest "choke point" on the planet. If the Japanese had actually deployed three or four of these boats in the mission they were designed for, it would have been catastrophic for the Allies!

The air-strike by nine (or twelve) high performance aircraft would have been a complete surprise, and it is easy to envision that the resulting damage to critical structures like locks and control facilities might have shut the canal down for weeks. Further, any shipping trapped in the Gulf of Panama would have been "sitting ducks" for such a powerful force.

If such a mission had been carried out, it would have required a major re-deployment of Allied ASW forces, and would certainly have relieved some of the pressure that Japanese forces were feeling elsewhere.

So, why didn't they do it?????

Well, .......It all comes back to the "tonnage war" being waged against Japanese shipping by the U.S. submarine fleet and the aircraft of the Air Force and Navy.

With the elimination of Japanese freighters, tankers, and transports, the Japanese were being forced to use their submarines in the same way the U.S. had been forced to use theirs in the beginning of the war: ...Re-supply and evacuation.

As a consequence of this need, boats like the Sen-Kotu class were being used as transports and cargo vessels, instead of waging the offensive war they had been designed for.


The term I-boat is really a most generic term. The Japanese built a bewildering variety of submarines during WWII, which was probably a serious mistake. If you count boats built between the wars, and their midget classes, the Japanese fielded no less than 34 different variations.

Rather than taking a successful design, and "running with it" (Like the Germans did with the TypeVII.) they kept coming up with radically different designs, building a few, and then deciding that they needed to do something else.
This is not to say that they didn't make some real advances: The Sen-Taka Class, developed towards the end of the war, had a submerged speed of 19 knots; ....making it probably the only WWII submarine that could run away from a German TypeXXI!

The picture below shows a Sen-Taka Class running at high speed on the surface.


The study of the Japanese Submarine War is a study in lost opportunities. Most of these were lost because of the schizophrenic nature of the Japanese Military Planning.

Time and time again, you see examples of logical, far-sighted planning: ...Pearl Harbor, the Invasion of the Philippines, and the U.S. West Coast submarine offensive, to name a few.

....But these logical plans kept being sidelined by the "Battleship Mentality" held by other members of that Japanese high command. They clung to the belief that they would fight one, glorious, decisive naval battle that would change the course of the War, and they insisted on diverting assets and resources in the pursuit of that forlorn hope.

If they had devoted even 25% of the resources they were pouring into "Super Battleships" (read dinosaurs) to their submarines, their fast, long range submarines would have been a force in the Pacific that could have changed the course of the War: .....Instead, their submarines were treated like the proverbial "red-haired stepson"!!!

Hell, ......the Japanese submarine service didn't even get radar until late 1944!! (After the War, one of the few surviving Japanese Sub Commanders was quoted as saying; "We wanted radar the way a man dying of thirst wants water!")

It's hard to imagine going up against late war Allied ASW technology without radar: ...but that is exactly what was happening. The demoralization that would result is easy to anticipate: .....And this probably explains the number of late war Japanese submarine patrol reports that documented 100 day patrols with "no contacts". http://forums.ubi.com/images/smilies/sadeyes.gif


03-05-2007, 03:28 PM
Another very interesting read this breif history of Japanese Subs. http://forums.ubi.com/images/smilies/clap.gif

The submarine aircraft carrier is truly awe inspiring but as said these subs were not utilised properly, they were wasted along with their brave crews.

Interesting note is that the Sen-Kotu was longer than it could dive, being 400ft long and a max depth of 330ft.
for example to put the Sen-Kotu vertical on end in the sea so that the bow is just under the surface the stern would be at crush depth !

Another quality post here from klcarrol http://forums.ubi.com/images/smilies/25.gif

03-05-2007, 04:40 PM
The British had an aircraft-carrying submarine a decade earlier - the M2. HERE (http://en.wikipedia.org/wiki/HMS_M2)