U.S. Navy
Wartime and Postwar
Fleet Boat Conversions

Fall 1944 Proposed Submarine Cargo Carrier (by Lockwood)

A stripped Fleet Boat capable of carrying 325 tons of cargo

Fall 1944 Proposed Submarine Tanker (by Lockwood)

A submarine with sufficient fuel capacity to top off at least four fleet submarines after they had expended 50% of their fuel.

Fleet Snorkel (SCB 47B)

312' length
27' 4” Beam
17' Draft
2,040 tons Surfaced Displacement
2,410 tons Submerged displacement
4,610 SHP Diesels, 2 Shafts
4,610 SHP Electric Motors, 2 Shafts
18 kt surfaced speed
9 kt submerged speed
400 ft Test Depth
81 to 83 crew

Weapons:
6 x 21” TT Bow
4 x 21” TT Stern
24 or 28 x 21” Torpedoes (Depending on whether
Balao or Tench was converted)

Boats Converted:
SS 302 Sabalo (Balao)
SS 303
Sablefish (Balao)
SS 320
Bergall (Balao)
SS 328
Charr (Balao)
SS 331
Bugara (Balao)
SS 337
Carbonero (Balao)
SS 338
Carp (Balao)
SS 348
Cusk (Balao)
SS 392
Sterlet (Balao)
SS 398
Segundo (Balao)
SS 399
Sea Cat (Balao)
SS 405
Sea Owl (Balao)
SS 408
Sennet (Balao)
SS 409
Piper (Balao)
SS 423
Torsk (Tench)
SS 475
Argonaut (Tench)
SS 476
Runner (Tench)
SS 480
Medregal (Tench)
SS 482
Irex (Tench)

GUPPY I

307' 7 length
27' 4” Beam
17' Draft
1,570 tons Surfaced Displacement
2,400 tons Submerged displacement
4,610 SHP Diesels, 2 Shafts
4,610 SHP Electric Motors, 2 Shafts
17.8 kt surfaced speed
18.2 kt submerged speed
400 ft Test Depth

Weapons:
6 x 21” TT Bow
4 x 21” TT Stern
22 x 21” Torpedoes

Boats Converted:
SS 484 Odax (Tench)
SS 486
Pomodon (Tench)

FY50 SSK Conversion (Type I)

306 length
27' 4” Beam
1,525 tons Surfaced Displacement
2,400 tons Submerged displacement
2,400 SHP Diesels, 2 Shafts
2,740 SHP Electric Motors, 2 Shafts
15 kt surfaced speed
9 kt submerged speed
300 ft Test Depth

Weapons:
4 x 21” TT Bow
4 x 21” TT Stern

Boats Converted:
SS 214 Grouper (Gato)

FY52 SSK Conversion (Type II)

306' 6” length
27' 2” Beam
2,400 tons Submerged displacement
3,800 SHP Diesels, 2 Shafts
2,740 SHP Electric Motors, 2 Shafts
17 kt surfaced speed
9 kt submerged speed
300 ft Test Depth

Weapons:
4 x 21” TT Bow
4 x 21” TT Stern

Boats Converted:
SS 240 Angler (Gato)
SS 241
Bashaw (Gato)
SS 242
Bluegill (Gato)
SS 243
Bream (Gato)
SS 244
Cavalla (Gato)
SS 246
Croaker (Gato)

GUPPY IA (SCB 47A)

307' 7 length
27' 4” Beam
17' Draft
1,800 tons Surfaced Displacement
2,400 tons Submerged displacement
5,400 SHP Diesels, 2 Shafts
4,610 SHP Electric Motors, 2 Shafts
18 kt surfaced speed
15 kt submerged speed
17,000 nm at 11 kts surfaced endurance
108 nm at 3 kt submerged endurance
400 ft Test Depth
79 to 84 crew

Weapons:
6 x 21” TT Bow
4 x 21” TT Stern
22 x 21” Torpedoes

GUPPY II (SCB 47)

307' 7 length
27' 4” Beam
17' Draft
2,040 tons Surfaced Displacement
2,400 tons Submerged displacement
4,610 SHP Diesels, 2 Shafts
4,610 SHP Electric Motors, 2 Shafts
18 kt surfaced speed
17.5 kt submerged speed
15,000 nm at 11 kts surfaced endurance
192 nm at 4 kt submerged endurance
400 ft Test Depth
84 to 85 crew

Weapons:
6 x 21” TT Bow
4 x 21” TT Stern
24 x 21” Torpedoes

Boats Converted:
SS 339 Catfish (Balao)
SS 343
Clamagore (Balao)
SS 344
Cobbler (Balao)
SS 345
Cochino (Balao)
SS 346
Corporal (Balao)
SS 347
Cubera (Balao)
SS 349
Diodon (Balao)
SS 350
Dogfish (Balao)
SS 351
Greenfish (Balao)
SS 352
Halfbeak (Balao)
SS 416
Tiru (Balao)
SS 425
Trumpetfish (Balao)
SS 426
Tusk (Balao)
SS 478
Cutlass (Tench)
SS 483
Sea Leopard (Tench)
SS 484
Odax (From Guppy I)
SS 485
Sirago (Tench)
SS 486
Pomodon (From Guppy I)
SS 487
Remora (Tench)
SS 490
Volador (Tench)
SS 522
Amberjack (Tench)
SS 523
Grampus (Tench)
SS 524
Pickerel (Tench)
SS 525
Grenadier (Tench)

GUPPY III (SCB 223)

321' length
27' 4” Beam
17' Draft
1,975 tons Surfaced Displacement
2,870 tons Submerged displacement
5,400 SHP Diesels, 2 Shafts
4,610 SHP Electric Motors, 2 Shafts
17 kt surfaced speed
16 kt submerged speed
15,900 nm at 8.5 kts surfaced endurance
108 nm at 4 kt submerged endurance
400 ft Test Depth
83 to 95 crew

Weapons:
6 x 21” TT Bow
4 x 21” TT Stern
24 x 21” Torpedoes

Boats Converted:
SS 343
Clamagore (GUPPY II Balao)
SS 344
Cobbler (GUPPY II Balao)
SS 346
Corporal (GUPPY II Balao)
SS 351
Green fish (GUPPY II Balao)
SS 416
Tiru (GUPPY II Balao)
SS 425
Trumpetfish (GUPPY II Balao)
SS 487
Remora (GUPPY II Tench)
SS 490
Volador (GUPPY II Tench)
SS 524
Pickerel (GUPPY II Tench)

Notes:
All the GUPPY IIs would have received this modernization under the FRAM program, but the program was curtailed to just nine boats.

FY48 Submarine Oiler (SSO) Conversion (SCB 39)

311' 7” length
38' 3” Beam
1,750 tons Surfaced Displacement
2,950 tons Submerged displacement
2,740 SHP Electric Motors, 2 Shafts
16 kt surfaced speed
7 kt submerged speed
300 ft Test Depth
76 Crew

Weapons:
2 x 21” TT Stern (6 Torpedoes)

Modifications Made:
    1.) One torpedo tube was left in the bow; but converted to a cargo discharge tube.
    2.) Electric motors replaced with quieter types; and Snorkel fitted.

Cargo Capacity:
585 tons (159,864 gallons) of liquid fuel (Saddle Tanks)

Employment:
Could also refuel submarines submerged, after hooking up fuel hoses on the surface. However, fuelling took ten hours, and the saddle tanks were easily breached if the submarine was bombed.

Notes: One Gato, the SS 362 Guavina, was converted.

FY48 Submarine Troop Carrier (SSP)

312' length
27' 4” Beam
1,525 tons Surfaced Displacement
2,410 tons Submerged displacement
2,305 SHP Diesels, 2 Shafts
2,740 SHP Electric Motors, 2 Shafts
14 kt surfaced speed
8 kt submerged speed
400 ft Test Depth
74 Crew

Weapons:
5”/25 (Bow) for shore bombardment
40mm (Bow Cigarette Deck) for shore bombardment

Cargo Capacity:
120 Troops
31 tons of cargo (Internal Hold)
21 tons of cargo (Deck Cargo)
1 x LVT with a Jeep and Pack Howitzer inside it carried in a pressure proof hangar, along with 8 x rubber boats

Modifications Made:
    1.) 3,000 PSI oxygen tanks were installed, providing 50,000 extra cubic feet of oxygen, along with a new CO2 scrubber.
    2.) All torpedo tubes were removed, as well as two main engines. The remaining engines were fitted with a snorkel.
    3.) Extra bunks, showers, and various accommodations were installed for the passengers.
    4). A Pressure-proof hangar capable of stowing one LVT inside was installed on the stern. A new hatch was installed in the submarine, enabling the hangar to be entered from below while still submerged.

Employment:
The USMC wanted a squadron of twelve of these boats to carry the 1,440 men of a USMC assault battalion ashore (120 men per SSP); along with four 75mm Pack Howitzers, six 57mm RCLs, five units of fire for each weapon (220 tons of ammo); and 158 tons of supplies for ten days. The infantry would land in rubber boats, but their equipment would have to be carried ashore by twelve LVTs, which were stowed inside the pressure-proof hangars; with a jeep and a 75mm howitzer already packed inside the LVT.

Boats Converted:
SS 313 Perch (Balao)
SS 315
Sealion (Balao)

FY48 Submarine Cargo Carrier (SSA)

312' length
27' 4” Beam
1,525 tons Surfaced Displacement
2,410 tons Submerged displacement
2,740 SHP Electric Motors, 2 Shafts
14 kt surfaced speed
9 kt submerged speed
400 ft Test Depth
61 Crew

Weapons:
6 x 21” TT Bow

Cargo Capacity:
28,300 gallons of gasoline (Tanks)

6,000 cubic feet of cargo stowage
or
120 tons of cargo

Modifications Made:
    1.) The forward pair of engines were removed; and a snorkel fitted.
    2.) The Aft torpedo tubes and all torpedo reloads deleted
    3.) A Large Diameter 36” hatch was added to access the main cargo space.
    4.) Two fuel tanks converted to carry gasoline.

Employment:
The USMC wanted these to support their raiders with supplies. A task force of 40 SSPs and SSAs could land a reinforced Marine Regiment.

Boats Converted:
SS 317 Barbero (Balao)

FY52 Submarine Minelayer (SSM) Conversion

Modifications To Be Made:
    1.) A 35 foot mine stowage plug would have been inserted between the forward battery and torpedo room.
    2.) A Streamlined Sail and Snorkel to be fitted.

Capacity:
108 x Mk 49 Mines in Dry Stowage in forward torpedo room, the mine plug, and the aft torpedo room
50 x Mk 49 Mines in Wet Stowage in modified main ballast tanks

Rationale:
Because existing submarines couldn't lay mines fast enough to make a dense field, or carry enough mines to make a large field, the SSM was proposed to fix this problem.

Boats Converted:
SS 382 Picuda (Balao) – Scheduled to be converted, but program cancelled, and Picuda GUPPYized instead.

Submarine Oiler (SSO) Conversion to support P6Ms (SCB 170)

Employment:
Could refuel a seaplane while submerged at 100 feet, at the rate of 400 gallons a minute via a floating buoy. Additionally, minor repairs on her seaplanes could be performed, as well as the boat acting as a navigational beacon.

Migrane I SSR Conversion

312' length
27' 4” Beam
1,525 tons Surfaced Displacement
2,410 tons Submerged displacement

Weapons:
4 x 21” TT Bow
1 x 40mm Deck Gun (Removed later

Electronics
SS Radar
SV-1 Radar
SV-2 Radar
AN/BPS-2 Radar
YE-2 Homing Beacon

Boats Converted:
SS 419 Tigrone (Tench)
SS 312
Burrfish (Balao)

FY 48 Migrane II SSR Conversion

312' length
27' 4” Beam
1,570 tons Surfaced Displacement
2,410 tons Submerged displacement
95 crew

Weapons:
4 x 21” TT Bow (two other tubes in bow are inactivated)
1 x 40mm Deck Gun (Removed later

Electronics
SS Radar
SV Radar
SV-2 Radar
SR-2 Radar
YE-3 Homing Beacon

Boats Converted:
SS 481 Requin (Tench)
SS 489 Spinax (Tench)

Migrane III SSR Conversion

341' 6” length
27' 4” Beam
1,700 tons Surfaced Displacement
107 crew

Weapons:
6 x 21” TT Bow
10 x 21” Long Torpedoes
2 x 21” Short Torpedoes

Electronics
AN/BPS-2
AN/BPS-3
AN/BPS-4

Boats Converted:
SS 267 Pompon (Gato)
SS 269
Rasher (Gato)
SS 270
Raton (Gato)
SS 271
Ray (Gato)
SS 272
Redfin (Gato)
SS 274
Rock (Gato)

FY48 JB-2 Loon SSG Conversion

312' length
27' 4” Beam
1,525 tons Surfaced Displacement
2,400 tons Submerged Displacement
84 crew

Weapons:
6 x 21” TT Bow
4 x 21” TT Stern

Boats Converted:
SS 348 Cusk (Balao)
SS 337
Carbonero (Balao)

Notes:
Original conversion had just a launching ramp aft and control equipment for use as a control ship. Later, a hangar for two Loons was fitted.

FY52 Regulus I SSG Conversion

312' length
27' 4” Beam
1,525 tons Surfaced Displacement
2,400 tons Submerged Displacement
3,430 SHP Diesels, 2 Shafts
2,740 SHP Electric Motors, 2 Shafts
84 crew

Weapons:
6 x 21” TT Bow
4 x 21” TT Stern
2 x Regulus I Missiles (Hangar)

Boats Converted:
SS 282 Tunny (Gato)

FY55 Regulus I SSG Conversion

312' length
27' 4” Beam
1,525 tons Surfaced Displacement
2,400 tons Submerged Displacement
2,305 SHP Diesels, 2 Shafts
2,740 SHP Electric Motors, 2 Shafts
84 crew

Weapons:
6 x 21” TT Bow
2 x Regulus I Missiles (Hangar)

Boats Converted:
SS 317 Barbero (Balao)

Notes:
Boat was converted from SSA

References:
The Fleet Submarine in the U. S. Navy: A Design and Construction History by John D. Alden
Cold War Submarines by Norman Polmar and K.J. Moore
US Submarines Through 1945 by Norman Friedman
US Submarines Post 1945 by Norman Friedman
US Amphibious Ships and Craft by Norman Friedman