References Consulted:

US Submarines, Post 1945 by Norman Friedman
US Destroyers, Second Edition by Norman Friedman
Adequacy of Current Organization: Defense and Arms Control – Appendix K by U.S. Government Publishing Office.
Rickover: Controversy and Genius – A Biography by Norman Polmar & Thomas B. Allen
N.S. Savannah Operating Experience by J.H. MacMillian, D.C. MacMillian, J.E. Robb, H.I. Lill, Jr, and R.O. Mehann (SNAME Transactions)
Nuclear Navy, 1939-1962 by Richard G. Hewlett and Francis Duncan, University of Chicago Press, 1975

Reactor Designations

From the early beginnings of the Navy's nuclear program to 1955; the Navy designated reactors by their application. For example, the reactor for the coming mass produced nuclear submarines was designated the Submarine Fleet Reactor, or SFR. The reactor being developed for aircraft carriers received the name Large Ship Reactor, or LSR.

This system, while functional for the early years of the Naval Reactor program, quickly became very confusing as more and more reactors were proposed. Thus in October 1955, Rickover's office issued a new system for designation naval reactors, reprinted below:

First Digit: Reactor Application

A: Aircraft Carrier
F: Frigate
C: Cruiser
D: Destroyer
S: Submarine

Second Digit: Number of reactors designed for that application by the manufacturer.

Third Digit: Manufacturer

C: Combustion Engineering
G: General Electric
W: Westinghouse
X: Unassigned (for conceptual future developments)

Combustion Engineering Reactors

S1C (Submarine Reactor, Small / SRS)

S2C

SSN 579 Tullibee Class

General Electric Reactors

S1G (Submarine Intermediate Reactor, Mark A / SIR MK A)

S2G (Submarine Intermediate Reactor, Mark B / SIR MK B)

SSN 575 Seawolf Class

S3G (Submarine Advanced Reactor, Prototype / SAR-1)

S4G (Submarine Advanced Reactor, Ship / SAR-2)

SSRN 586 Triton Class

S5G

Power
17,000 SHP

Service Life:
10,000 hours at full power

Uses:
SSN 671 Narwhal Class

S6G

Power
30,000 SHP

Uses:
SSN 688 Los Angeles Class

S7G

Notes: Prototype Land-based reactor which did not use control rods; reactivity being controlled by stationary gadolinium tubes partially filled with water. Water could be pumped from the portion of the tube inside the core up to a reservoir above the core, or allowed to flow back down into the tube. A higher water level in the tube slowed more neutrons in the core, causing more neutron capture by the gadolinium tube cladding rather than by the uranium fuel, thus lowering the power level. The system was configured with the pump running continually to keep the water level low; on loss of electrical power, all of the water would flow back into the tube, shutting down the reactor.

S8G

Uses:
SSBN 726 Ohio Class

Notes: Natural-circulation/Forced Circulation reactor. At low power levels, coolant is allowed to circulate via heat differential. At higher power levels, pumps kick in.

S9G

Uses:
SSN 774 Virginia Class

Core Lifetime:
33 Years

D1G

Notes: Land-Based Prototype for D2G.

D2G

Uses:
CGN 25 Bainbridge
CGN 35 Truxtun
CGN 36 California Class
CGN 38 Virginia Class

Output:
30,000 SHP

Westinghouse Reactors

A1W (Large Ship Reactor, Prototype / LSR)

Notes: Land-Based prototype for A2W. Two reactors were built; A1W-A and A1W-B.

A2W (Large Ship Reactor, Ship / LSR)

Uses:
CVN-65 Enterprise

Output:
35,000 SHP per Reactor.

Installation on Enterprise:
A2W-1A
A2W-1B
A2W-2A
A2W-2B
A2W-3A
A2W-3B
A2W-4A
A2W-4B

A3W

Uses:
CVN 67 John F. Kennedy (cancelled)

Notes: Was built for CVN-67; but she was re-ordered as CV-67. The layout for CVN-67 would have been four reactors; a reduction by half of the eight needed for Enterprise.

A4W

Uses:
CVN 68 Nimitz Class
CVN 71 Theodore Roosevelt Class

Output:
130,000 SHP per Reactor.

Notes: Another reduction in reactor numbers was achieved; with only two reactors being needed for the Nimitz class.

C1W

Uses:
CGN-9 Long Beach

Output:
40,000 SHP per Reactor.

F1W

Notes: Frigate reactor using an A1W core.

S1W (Submarine Thermal Reactor Mark I / STR MK I)

Land Based Prototype for S2W.

S2W (Submarine Thermal Reactor Mark II / STR MK II)

Service Life:
900 hours at full power

Uses:
SSN 571 Nautilus Class

S3W (Submarine Fleet Reactor / SFR)

Service Life:
2,000 hours at full power (Early)
2,500 hours at full power (Late)

Uses:
SSN 578 Skate Class
SSGN 587 Halibut Class

S4W (Submarine Fleet Reactor /SFR)

Uses:
SSN 579 Swordfish
SSN 584 Seadragon

Notes: Was a variant of the S3W with horizontal steam generators used in the S1W and S2W. During overhauls both boats which had been built with the S4W had it replaced with the S5W.

S5W (High Speed Submarine Reactor)

Service Life:
5,500 hours at full power (Early Cores)
10,000 hours at full power (Later Cores)

Uses:
1955 BuShips LSST
SSN 585 Skipjack Class
SSN 593 Thresher/Permit Class
SSBN 598 George Washington Class
SSBN 608 Ethan Allan Class
SSBN 616 Lafayette Class

S6W

Uses:
SSN 21 Seawolf

Bechtel Reactors

A1B

Uses:
CVN 78 Gerald R. Ford Class

Reactor Developmental Designations

C1X (Cruiser Reactor)

D1X (Task Force Escort Reactor / FER)

Civilian Reactors

N/S Savannah Reactor

Service Life:
52,200 MW/d (original design value)
42,000 MW/d (later, revised design value), equal to 568 days at full power

Uses:
N/S Savannah