[WWII] Amphibious submarine (fictional)

[copeab]

Amphibious Submarine
Copyright 2012 by Brandon Cope

The origin of the amphibious submarine design was Professor Eric Wessler. He saw the combination of a midget submarine and walker as a useful scout unit to naval forces. The Kreigsmarine was not overjoyed at the project, but Hitler was, seeing possible uses not on the high seas but in Europe, in the invasions of England and Russia. Development was problematic, however, and the first working prototype didn't appear until March 1941. By that time, Hitler had lost interest and funding was canceled. However, at one of the few demonstrations to military and government officials, a Japanese naval officer was present.He excitedly relayed the news of the invention to Tokyo, where the concept was greeted with excitement. The Japanese obtained rights to the design and made several improvements *including reduction to a more practical size), but were able to field operational units by March 1942.

The Japanese sailors called it the koebi (shrimp) and used all they had in scouting Pacific islands. Due to their short range, they had to be carried most of the way on the rear decks of larger submarines or the sterns of surface vessels, which usually required the surface ship to have to remove a primary gun turret. In a few cases, the amphibious sub was towed rather than carried..

The 20mm gun in the turret is primarily intended for use against aircraft but can also be used against ground forces. The four machine guns are all "tail chasers", intended to discourage pursuit if the vehicle must retreat to water. There are two hatches on the deck, one over the engine compartment and one over the bridge. Next to the bridge (main) hatch is a mount for the searchlight, which is normally stowed internally.

The amphibious submarine has a crew of five. The 20mm gunner (who also serves as mechanic) manually rotates his turret at 12.5 degrees per second.. The engines burn 2.4 gallons of diesel fuel per hour of routine usage. The koebi can travel 580 miles at 7 mph surfaced and 40 miles at 3 mph submerged.

Subassemblies: Large Boat chassis with Sub option +4, 8xsealed Very Heavy Walker Legs +2, full-rutation Medium Weapon turret. +1
Powertrain: 60-kW marine diesel engine with 60-kW water screw and 201-gallon standard tanks; 35-kW electric motor with 35-kW water screw; 60-kW leg transmission, 45,000-kWs batteries†.
Occupancy: 5 CS Cargo: 5

Armor
Body/Legs/Turret: 4/20

Weaponry
4xGroundMG [Body:B] (500 each).
20mm Long Ground AC [Tur:F] (225).

Equipment
Body: Autopilot; bilge pump; 5xbilge, fire extinguisher†; 10-man-days life support†; navigation instruments; precision navigation instruments; 10-man/days of provisions; 10’ 5¥ periscope; large radio receiver and transmitter; medium radio receiver and transmitter; mini-searchlight. Turret: Universal mount.
† Limited access.

Statistics
Size: 27’¥6’¥12’
Payload: 1.3 tons
Lwt: 21.3 tons
Volume: 197
Maint.: 30 hours
Price: $44,000
HT: 8
HP: 750 [Body], 75 [turret], 112 [each leg]

wSpeed: 11.5
wAccel: 0.1
wDecel: 0.5(0.6)
wMR: 0.1
wSR: 2
Draft: 2.3'
Flotation Rating 22 tons.

uSpeed: 6.5
uAccel: 0.1
uDecel: 0.3(0.4)
uMR: 0.1
uSR: 2
uDraft: 12;
Crush Depth 65 yards.

gSpeed: 20
gAccel: 1
gDecel: 10
gMR: 0.5
gSR: 3
Low Ground Pressure. 4/5 Off-Road Speed.

Design Notes
While the legs tuck against the sides and underbody of the submarine in the water, they have a negative impact on hydrodynamics, Underwater, it uses a 3 rather than 4 divisor and on the surface a 10 in the Drag formulas.

The gap between the turret and periscope/radio antenna is just enough for the cannon barrel to not strike either. However, it does create a small dead spot to the front for the 20mm cannon. Additionally, an excited gunner could shoot either periscope or antennas if not paying attention. The turret is retractable and not sealed (but it is waterproofed). Diving with it extended could have disastrous results ...

The machine gun muzzles are behind water-tight doors that must be opened before they fire. Not opening the doors first results in the bullets striking DR 20 panels. Failure to seal the doors before entering water doesn't endanger the boat, but completely soaks the guns and their ammo, which could lead to malfunctions.

The mini-searchlight has a range of 2 miles. It is $20, 40 lbs and 0.15 VSP.

Variants
Some were built with four more machine guns in the hull, facing forward. These actually suffered more losses, as the commander was more tempted to fight it out with enemy forces he came across.

[Anaraxes]

Why legs?

There were real-world proposals for wheeled submarines, though I don't know if they were ever actually built. And in the 1980s, the Soviet navy was supposed to be intruding upon Swedish territorial waters with (among other things) submarines with bottom-crawling capability, though with catepillar treads.

Just Rule of Cool?

[copeab]

Originally Posted by Anaraxes

Why legs?

Mostly Rule of Cool, although I think legs are better for transitioning from water to land than wheels. I did first consider tracks, but this would have been slightly trickier to do with MVDS than in VE2.

[Anaraxes]

If nothing else, legs give you the great "shrimp" image.

[copeab]

Originally Posted by Anaraxes

If nothing else, legs give you the great "shrimp" image.

Originally it was going to be a German vehicle named the hummer (lobster).

[copeab]

I was asked on a mailing list if the koebi can power the legs with the electric motor (to reduce vehicle noise). I actually hadn't considered that. If the diesel can power the legs and screw, I don't see why the electric motor can't as well.

However, due to the lower output of the electric motor, it can only get the koebi up to about 15 mph on the legs.

(thanks John D.)

Also, I suppose, in the watet the vehicle could use both screws (diesel) and legs (electric motor) for propulsion to get a slight boost in speed …

[Ed the Coastie]

I am going to have to use this concept in a future game. The German variant would fit almost perfectly in the Antarctic Redoubt / Hollow Earth corner of my campaign.

[copeab]

Originally Posted by Ed the Coastie

I am going to have to use this concept in a future game. The German variant would fit almost perfectly in the Antarctic Redoubt / Hollow Earth corner of my campaign.

I didn't work out the original prototype, but I imagined it being a small U-boat, perhaps a Typ II, with legs added.

Even with that, there is nothing in the design that is exclusively Japanse. The vehifle could be built and operated by many of the combatants in a Weird War II setting.