I-400 submersible carrier [Japan]

copeab · 12-16-2005, 07:12 AM

This was probably my favorite vehicle of the book. It was also the largest.
----------------------------
STo-class submersible carrier
Copyright 2005 by Brandon Cope

Although several nations had toyed with submarine-launched aircraft since WWI, in WWII only Japan mounted offensive operations using such submarine/aircraft combinations (see the E14Y “Glen” on p.W:MP97) and operated some 40 submarines that carried one or more seaplanes capable of dropping bombs or torpedoes (the most numerous being the B1, p.W:MP122).
The largest of these submarine classes was the STo class (also known as the I-400 class from the first-of-class), the biggest operational subs of WWII (only modern ballistic missile subs are normally much larger). Initially designed for a raid on the Panama Canal, other targets were later considered but the war ended before any attacks could be carried out.

The most distinctive feature of the class was a 114' long, 18' cylinder mounted atop the deck that housed four M6A1 Serian single-engine, twin-seat seaplanes (three partially disassembled and parts for a fourth) and an 85’ launch ramp equipped with catapult on the forward deck. These planes were developed specifically for the STo-class and, despite some poor quality control, were the best planes ever carried by a submarine. In theory, three planes could be launched within 15 minutes of surfacing, although this included arming the planes and warming the engines in the hangar while submerged. Four torpedoes, three 1,700-lb bombs, and twelve 550-lb bombs were carried to arm the aircraft. The location of the hangar required the conning tower to be offset several feet from the centerline, which caused the submarines to pull to the left when moving submerged with the rudders straight.

Only the I-400 and I-401 were completed as planned; the I-402 was finished as a tanker. Two others were scrapped during construction and thirteen more were simply cancelled. The hull was coated with rubber to reduce radar signature. Like many late-war subs, it carried a heavy AA armament. The two STo-class ships were somewhat slow to surface, taking nearly a minute. The American prize crews who sailed them after surrender reported that they handled well on the surface, even in poor weather, but were not allowed to submerge.

At one point, after the Panama Canal was dismissed as a target, consideration was given to attacking a city along the American West Coast, with San Francisco as the primary target, with biological weapons. However, this was called off as it was believed that such an attack would anger the Americans too much. There was also rumored to be a plan to use the uranium oxide carried aboard U-234 (p.WW121) to create "dirty" bombs to be used on San Francisco. As the German U-boat was captured in mid-May of 1945, the plan, if there had been one, was cancelled.

The I-400 has a listed crew of 144, but when surrendered in late August 1945 had over 200 men on board. Supposedly the extra men were to aid in aircraft operations. The I-400 has eight 533mm torpedo tubes, in two four-tube sections in the bow. The secondary armament consists of a 140mm gun in an open mount (2∞/s manual traverse). Three triple 25mm autocannons open mounts were installed over the hangar and a single 25mm autocannon in an open mount was located at the rear part of the conning tower (15∞/s manual traverse).

The engines burn 229 gallons of diesel fuel per hour of routine usage. Fuel, ammo, and provisions cost $200,000.

I-400

Subassemblies: Heavy Destroyer chassis with Sub option +8; sealed Huge Naval Secondary hangar [Body:T] +6; Medium Secondary Superstructure [Body:T] +4; three full-rotation Large Weapon open mounts [Body:T] +2; full rotation Medium Weapon open mount [Sup:T] +1; full rotation Medium TD open mount +3.
Powertrain: 4¥1,432-kW marine diesel engines with 2¥2,864-kW water screws and 300,000-gallon standard tanks; 2¥1,567-kW electric motors with 20.4 million-kWs batteries†.
Occ: See above Cargo: 776 Body, 1,700 Hangar, 94 Superstructure.

Code:

Armor	F	RL	B	T	U
Body:	4/60	4/60	4/60	4/60	4/60
Sup:	4/60	4/60	4/60	4/60	-
Hang:	4/60	4/60	4/60	4/60	-

Weaponry
140mm Medium DP Gun/11 Shiki [OM1:F] (300 rounds).
9¥25mm Med. Ground AC/Type 96 [OM2-4:F] (1,000 rounds each).*
1¥25mm Med. Ground AC/Type 96 [OM5:F] (1,000 round each).
8¥533mm Torpedo Tubes [Body:F].(20)**
* Linked in triplets. ** Linked in quadruples.

Equipment
Body: Autopilot; 2¥backup driver controls; 16,000-VSP bilge; 44¥bilge pumps†; 70¥bunks; cabin; 1,100-VSP cargo holds; 225-man environmental control†; fire direction center; 36¥fire extinguishers†; 144-man-days life support†; navigation instruments; precision navigation instruments; 15,300-man/days of provisions; 2-mile passive sonar. Hangar: 8,400-gallon standard fuel tank (aviation fuel). Sup: Navigation instruments; 2¥40’ 15¥ periscopes; large radio direction finder; 2¥very large radio receivers and transmitters; searchlight. OM2-5: Universal mount.
† Limited access.

Code:

Statistics
Size: 400'¥39'¥54'	Payload: 989 tons	Lwt.: 5,248 tons
Volume: 36,230	Maint: 8	Price: $663,000

HT: 8. HPs: 150,000 Body, 4200 Hangar, 750 Sup, 360 OM1, 120 each OM2-4, 75 OM5.

Code:

wSpeed: 22	wAccel: 0.2	wDecel: 0.5(0.6)	wMR: 0.05	wSR: 5
Draft 23'. Flotation Rating 5,248 tons. 
uSpeed: 7	uAccel: 0.1 uDecel: 0.5(0.6)	uMR: 0.05	uSR: 5
uDraft 54'. Crush Depth 100 yards.

Design Notes
The 6,560-ton historical submerged weight was used for underwater performance.

Fiergo · 12-17-2005, 09:06 AM

Nice Copeab, I always wondered what this thing would look like in GURPS terms. I usually don't make naval vessels because it takes so much time and detail (have to remember things like adequate living quarters, appropriate amount of bilge space, environmental conditions, etc.). Well done.

Kale · 12-17-2005, 09:36 AM

That's a pretty scary ship! If it could remain submerged for long periods it would have been handy for surgical strikes. Any idea about the stats for the planes?

copeab · 12-17-2005, 09:42 AM

Quote:

Originally Posted by Kale

That's a pretty scary ship! If it could remain submerged for long periods it would have been handy for surgical strikes. Any idea about the stats for the planes?

http://www.nasm.si.edu/research/aero...chi_serian.htm

And yes, I typoed the name.

From what I've read about a US "trophy" crew sailing the I-400 to a US-controlled base, they said it handled fairly well on the surface (they were forbidden to submerge).

Kale · 12-17-2005, 12:50 PM

Quote:

Originally Posted by copeab

From what I've read about a US "trophy" crew sailing the I-400 to a US-controlled base, they said it handled fairly well on the surface (they were forbidden to submerge).

Well, a large ship is going to be more stable than a small one on the high seas.

Toubrouk · 12-17-2005, 09:59 PM

Just an idea; in a game of Weird War II, we can pack a lot of "Fun" stuff in those submersible carriers.

I can imagine mecha, doomsday cruise missiles, geneticaly enhanced monsters, zombies...

flyingwombat · 12-18-2005, 02:33 AM

Quote:

Originally Posted by copeab

This was probably my favorite vehicle of the book. It was also the largest.

At one point, after the Panama Canal was dismissed as a target, consideration was given to attacking a city along the American West Coast, with San Francisco as the primary target, with biological weapons. However, this was called off as it was believed that such an attack would anger the Americans too much.

Really? Why would the Japanese care at that late date? They didn't care about our anger when they attacked Pearl Harbor etc.
I'm not doubting the source. I just find it strange.

Xenarthral · 12-18-2005, 03:05 AM

Quote:

Originally Posted by flyingwombat

Really? Why would the Japanese care at that late date? They didn't care about our anger when they attacked Pearl Harbor etc.
I'm not doubting the source. I just find it strange.

I've been lead to believe that the idea was that the anger would be mitigated
by the lack of a Pacific fleet to use in retaliation.

copeab · 12-18-2005, 03:25 AM

Quote:

Originally Posted by flyingwombat

Really? Why would the Japanese care at that late date? They didn't care about our anger when they attacked Pearl Harbor etc.
I'm not doubting the source. I just find it strange.

On Dec 7, 1941, the US wasn't capable of launching B-29 raids on Japanese cities.

Z09SS · 12-19-2005, 01:14 AM

They weren't worried about angering us because it was believed that we would be cowed by their might. Yamamoto's "Waking a sleeping giant" was thought of as alarmist.

12-16-2005, 07:12 AM	#1
copeab Join Date: Mar 2005 Location: near Houston	I-400 submersible carrier [Japan] This was probably my favorite vehicle of the book. It was also the largest. ---------------------------- STo-class submersible carrier Copyright 2005 by Brandon Cope Although several nations had toyed with submarine-launched aircraft since WWI, in WWII only Japan mounted offensive operations using such submarine/aircraft combinations (see the E14Y “Glen” on p.W:MP97) and operated some 40 submarines that carried one or more seaplanes capable of dropping bombs or torpedoes (the most numerous being the B1, p.W:MP122). The largest of these submarine classes was the STo class (also known as the I-400 class from the first-of-class), the biggest operational subs of WWII (only modern ballistic missile subs are normally much larger). Initially designed for a raid on the Panama Canal, other targets were later considered but the war ended before any attacks could be carried out. The most distinctive feature of the class was a 114' long, 18' cylinder mounted atop the deck that housed four M6A1 Serian single-engine, twin-seat seaplanes (three partially disassembled and parts for a fourth) and an 85’ launch ramp equipped with catapult on the forward deck. These planes were developed specifically for the STo-class and, despite some poor quality control, were the best planes ever carried by a submarine. In theory, three planes could be launched within 15 minutes of surfacing, although this included arming the planes and warming the engines in the hangar while submerged. Four torpedoes, three 1,700-lb bombs, and twelve 550-lb bombs were carried to arm the aircraft. The location of the hangar required the conning tower to be offset several feet from the centerline, which caused the submarines to pull to the left when moving submerged with the rudders straight. Only the I-400 and I-401 were completed as planned; the I-402 was finished as a tanker. Two others were scrapped during construction and thirteen more were simply cancelled. The hull was coated with rubber to reduce radar signature. Like many late-war subs, it carried a heavy AA armament. The two STo-class ships were somewhat slow to surface, taking nearly a minute. The American prize crews who sailed them after surrender reported that they handled well on the surface, even in poor weather, but were not allowed to submerge. At one point, after the Panama Canal was dismissed as a target, consideration was given to attacking a city along the American West Coast, with San Francisco as the primary target, with biological weapons. However, this was called off as it was believed that such an attack would anger the Americans too much. There was also rumored to be a plan to use the uranium oxide carried aboard U-234 (p.WW121) to create "dirty" bombs to be used on San Francisco. As the German U-boat was captured in mid-May of 1945, the plan, if there had been one, was cancelled. The I-400 has a listed crew of 144, but when surrendered in late August 1945 had over 200 men on board. Supposedly the extra men were to aid in aircraft operations. The I-400 has eight 533mm torpedo tubes, in two four-tube sections in the bow. The secondary armament consists of a 140mm gun in an open mount (2∞/s manual traverse). Three triple 25mm autocannons open mounts were installed over the hangar and a single 25mm autocannon in an open mount was located at the rear part of the conning tower (15∞/s manual traverse). The engines burn 229 gallons of diesel fuel per hour of routine usage. Fuel, ammo, and provisions cost $200,000. I-400 Subassemblies: Heavy Destroyer chassis with Sub option +8; sealed Huge Naval Secondary hangar [Body:T] +6; Medium Secondary Superstructure [Body:T] +4; three full-rotation Large Weapon open mounts [Body:T] +2; full rotation Medium Weapon open mount [Sup:T] +1; full rotation Medium TD open mount +3. Powertrain: 4¥1,432-kW marine diesel engines with 2¥2,864-kW water screws and 300,000-gallon standard tanks; 2¥1,567-kW electric motors with 20.4 million-kWs batteries†. Occ: See above Cargo: 776 Body, 1,700 Hangar, 94 Superstructure. Code: Armor F RL B T U Body: 4/60 4/60 4/60 4/60 4/60 Sup: 4/60 4/60 4/60 4/60 - Hang: 4/60 4/60 4/60 4/60 - Weaponry 140mm Medium DP Gun/11 Shiki [OM1:F] (300 rounds). 9¥25mm Med. Ground AC/Type 96 [OM2-4:F] (1,000 rounds each).* 1¥25mm Med. Ground AC/Type 96 [OM5:F] (1,000 round each). 8¥533mm Torpedo Tubes [Body:F].(20)** * Linked in triplets. ** Linked in quadruples. Equipment Body: Autopilot; 2¥backup driver controls; 16,000-VSP bilge; 44¥bilge pumps†; 70¥bunks; cabin; 1,100-VSP cargo holds; 225-man environmental control†; fire direction center; 36¥fire extinguishers†; 144-man-days life support†; navigation instruments; precision navigation instruments; 15,300-man/days of provisions; 2-mile passive sonar. Hangar: 8,400-gallon standard fuel tank (aviation fuel). Sup: Navigation instruments; 2¥40’ 15¥ periscopes; large radio direction finder; 2¥very large radio receivers and transmitters; searchlight. OM2-5: Universal mount. † Limited access. Code: Statistics Size: 400'¥39'¥54' Payload: 989 tons Lwt.: 5,248 tons Volume: 36,230 Maint: 8 Price: $663,000 HT: 8. HPs: 150,000 Body, 4200 Hangar, 750 Sup, 360 OM1, 120 each OM2-4, 75 OM5. Code: wSpeed: 22 wAccel: 0.2 wDecel: 0.5(0.6) wMR: 0.05 wSR: 5 Draft 23'. Flotation Rating 5,248 tons. uSpeed: 7 uAccel: 0.1 uDecel: 0.5(0.6) uMR: 0.05 uSR: 5 uDraft 54'. Crush Depth 100 yards. Design Notes The 6,560-ton historical submerged weight was used for underwater performance. __________________ A generous and sadistic GM, Brandon Cope GURPS 3e stuff: http://copeab.tripod.com

12-17-2005, 09:06 AM	#2
Fiergo Join Date: Nov 2005	Re: I-400 submersible carrier [Japan] Nice Copeab, I always wondered what this thing would look like in GURPS terms. I usually don't make naval vessels because it takes so much time and detail (have to remember things like adequate living quarters, appropriate amount of bilge space, environmental conditions, etc.). Well done.

12-17-2005, 09:36 AM	#3
Kale Join Date: Aug 2005 Location: Cowtown, Canada	Re: I-400 submersible carrier [Japan] That's a pretty scary ship! If it could remain submerged for long periods it would have been handy for surgical strikes. Any idea about the stats for the planes?

12-17-2005, 09:59 PM	#6
Toubrouk Join Date: Nov 2005 Location: Montreal, Canada.	Re: I-400 submersible carrier [Japan] Just an idea; in a game of Weird War II, we can pack a lot of "Fun" stuff in those submersible carriers. I can imagine mecha, doomsday cruise missiles, geneticaly enhanced monsters, zombies...

12-19-2005, 01:14 AM	#10
Z09SS Join Date: Jul 2005 Location: Holiday, FL	Re: I-400 submersible carrier [Japan] They weren't worried about angering us because it was believed that we would be cowed by their might. Yamamoto's "Waking a sleeping giant" was thought of as alarmist. __________________ A hobbyist is an expert in their hobby. Unaccredited to be sure, but an expert nonetheless!