[gurps] I-400 (was Re:TL6? Sub Carriers)

[Brandon Cope]

--- Eric Funk
<eric_funk_anti_spam_this_is_a_real_email_address at r3d.net>
wrote:

> I just watched a documentary on the japanese i-400
> submarine aircraft 
> carriers designed to attack the Panama Canal from
> the East. Is there 
> anything special to do to design them in GURPS?
> 
> Install vehicle bays in the sub, and transformable
> components in the Aichi 
> M6A Seiran aircraft's wing components?

I did the design a few years ago using the WWII MVDS.
-----------------------------------------------------
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&#8734;/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&#8734;/s manual traverse).

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

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.

Armor
Body/Superstructure/Hangar: 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.

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. 

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 
---------------
The M6 floatplane can be found at:

http://www.geocities.com/copeab/Vehicles/M6ASeiran.html

Brandon