First-Generation US Nuclear Submarines

I find the introduction/implementation of new technologies very fascinating.  When these new technologies are first unleashed, there is a great deal of variety and plenty of experimentation going on before everyone falls into line and starts building very similar things.  The initial deployment of a new technology leads to some really interesting decisions and designs though.

This post is about the impact of nuclear power on submarine design, and on operation. Both were impacted in major ways, and it took several years for builders and sailors to sort things out.  In the meantime, the first generation nuclear boats were somewhat experimental.  There was quite a bit of variety in design and purpose for the new ships.

Until the advent of nuclear power, the best submarine in the world had been built by Germany during World War II.  This was the remarkable Type XXI U-Boat.  These submarines were built from 1943 to 1945, but although superior to any other submarine were plagued by quality control problems, and also by wartime bombing of the production factories.

These submarines incorporated massive storage batteries for enhanced underwater endurance, allowing them to stay submerged at 5 knots for 2-3 days straight.  Additionally, the Type XXI was equipped with a "Schnorkel" (the snorkel mast), which allowed it to remain submerged while running diesel generators to recharge the batteries.  Most importantly, they were fast and quiet, compared to their peers.

Below, Type XXI submarines moored at Bergen, Norway.  May 1945.

There is only one surviving Type XXI submarine, which was scuttled and then re-floated.  It is located at the German Maritime Museum in Bremerhaven.  Photo below.

The advanced technology developed for the Type XXI was not lost on anyone.  After World War II ended, the US Navy tested and Reverse-Engineered two German U-Boats, the U-2513 and U-3008.  As a result, several engineering goals were identified and used in the design of new US submarines.  Those goals were:

1. Streamlining the hull
2. Improving Battery Capacity
3. Installing Snorkels
4. Improving fire control systems

The Navy immediately wanted to begin building a brand new class of submarine with all the new features, but the Bureau of Ships felt that the plethora of WW II submarines could be modified enough to reach most of the goals.  Thus was born the GUPPY program, a series of modifications to improve US Tench, Balao, and Gato class WWII fleet boats, to make them perform more like a German Type XXI.

Below, a Tench Class Fleet Boat, the USS Toro.  The deck guns have not yet been installed for a war patrol.  Note the clutter on the deck and conning tower.

GUPPY mods included rounding the bow, removing the deck guns, and placing a fairing around the conning tower - which was afterwards called a "sail".  Snorkel masts were installed on ships that could accommodate them, and larger capacity batteries were installed.  The last GUPPY conversion was completed in 1963, by which time the WWII ships were no longer able to confront more modern enemy subs.

Below, the USS Tench with Guppy 1 Modification.  Rounded bow, very litle deck clutter.  Antennae and periscopes enclosed in a streamlined sail.

Meanwhile the Navy had managed to fund a few brand-new submarines, starting in 1946, with all of the features from their German Type XXI wish list.  These were the six Tang class submarines.  The Tang class were very capable ships:  The range without refueling was 10,000 miles.  They could run 15 knots surfaced, 18 knots submerged, and could dive to 700 ft.  Far better than anything a WWII fleet boat could do - including a Type XXI.

Nevertheless, all diesel-electric submarines, regardless of their sophistication, need to snorkel and burn diesel fuel to recharge their batteries.  During these periods of charging the batteries (which occur frequently), the submarine is much more exposed to detection than when operating deep. Additionally there is increased danger to a submarine spending long periods at periscope depth from collision with surface vessels, who will be unaware that a submarine is nearby.  The snorkel mast is made intentionally difficult to spot or to detect on radar.  These are the operating limits of a submarine that relies on internal combustion engines to function.

The USS Wahoo, a Tang-Class submarine.

And then suddenly the world changed, and many of the things submarine designers and sailors had always contended with were thrown out the window.

Below: The ship that changed everything - USS Nautilus at her launch on 21 January 1954...  On January 17, 1955 she was "Underway on nuclear power".

The new nuclear propulsion system did several things for ship designers.  No longer did they need to give top design priority to battery capacity, massive multiple diesel generator sets (for quickly charging the batteries), and setting aside space for large quantities of diesel fuel. The new propulsion system allowed engineers to explore the capabilities of a ship that was independent of internal combustion. And explore they did...

Below, the power plant that started it all.  The S1W prototype reactor in Idaho.  The water tank surrounding the reactor compartment is to absorb gamma radiation and to slow and absorb neutrons. The reactor is well shielded internally and unshielded (except for the pressure hull) exernally.

With all that history out of the way, we finally reached to the subject of this post!

USS Nautilus made a shakedown cruise four months after her first nuclear-powered underway.  Submerged the entire time, she ran 1300 miles from New London Connecticut, to San Juan, Puerto Rico, covering it in less than 90 hours.  This was the longest submerged cruise ever made by a submarine and the highest sustained speed ever recorded.

Nautilus' incredible speed and endurance rendered most of the Anti-Submarine warfare tactics that had been developed during World War II obsolete.  Radar and anti-submarine spotting aircraft were useless against a ship that no longer had to be near the surface and extend a snorkel mast to recharge the main storage batteries.  It could also quickly change position and depth.  A new and difficult adversary, which is difficult to detect and defeat, even today.

Nautilus (SSN-571) against New York backdrop.  SSN stands for Submersible Ship, Nuclear

On October 4, 1957, the Soviet Union placed the Sputnik satellite into orbit, shocking the entire nation.  The implicit message for the US was that the Soviets could rain down nuclear weapons on any US city at any time.

In August 1958, Nautilus was the first ship to reach the North Pole.  She passed through the Bering Strait, and dove under the ice for 2 days before reaching the pole, then continued on toward Greenland.  She did not break the ice during the trip - it was done entirely submerged.

The implicit message for the Soviet Union was that nuclear-powered ballistic missile subs (which were then under construction) could hide under the polar ice and rain down nuclear weapons on any Soviet city at any time.  And thus began the early pieces of what eventually came to be known as "mutually assured destruction"

Nautilus - aside from her novel power source - was not an awesome warship or nuclear deterrent.  The hull and superstructure vibrated so badly that her sonar became useless at anything over 4 knots.  The lessons learned were modified in later designs.

While Nautilus was a ground-breaking ship, in reality she was also a simple old-school Tang-Class diesel submarine with a pressurized water reactor instead of diesel generators.

Let's look at another first-generation nuclear boat.

USS Seawolf (SSN-575) underway surfaced.

Seawolf was similar in many respects to the Nautilus.  She was also a Tang-Class submarine with a nuclear reactor instead of diesel-electric components.  She was commissioned in March of 1957.  This ship used a much more advanced nuclear propulsion system - one that turned out to be overly complex and maintenance intensive.

Seawolf was powered by the S2G liquid-sodium cooled reactor.  By using liquid sodium, the reactor primary coolant system could be operated at higher temperature and much lower pressure.  Also because liquid metal can remove more heat more efficiently than water, steam could be superheated, raising efficiency even further.

The primary coolant system operated at only 15 psig, so the cooling system was quite light.  However... The superheaters suffered from poor tubesheet welds and frequently leaked high pressure steam backwards into the liquid sodium coolant.  This leakage of water into hot liquid sodium created a reaction that caused formation of sodium hydroxide (a strong caustic) and hydrogen gas (explosive when mixed with air).

An additional concern was that the sodium coolant could never be allowed to lose heat.  Dropping below the melting point would freeze the coolant, resulting in a loss of circulation.  Loss of circulation is never a good thing in a reactor core.

In 1960 Seawolf's power plant was converted to an S2W reactor, and with that, the experiment ended!

The Skate (SSN-578) was the third nuclear-powered submarine launched by the US, and the lead ship of only four in that class.  This made the Skate class the first actual production run of nuclear submarines. All ships of this class used the S3W reactor.

Below, USS Skate surfaced at the north pole, August 1959.  Note the steam rising from the warm seawater discharge at the right side of the photo.

Skate was commissioned in December of 1957, and in August 1959, became the first submarine to surface at the north pole.  In August of 1962, Skate and Seadragon rendezvoused at the north pole and surfaced together.  They operated together for another week before parting ways.

The ships of this Class were Skate, Sargo, Seadragon and Swordfish.  Even though the power plant had changed dramatically, this series of submarines was still based on incremental improvements of the German Type XXI diesel boat!

Change was in the works regarding hull design, however.  Importantly for the new nuclear-powered submarines, a prototype diesel-electric submarine had been testing the advantages of streamlining for optimum underwater performance.  This ship was the "Auxiliary Submarine" AGSS Albacore .  Her hull was the result of wind-tunnel testing, and she revolutionized submarine design by using a teardrop shaped hull, thus minimizing drag.

Albacore at launch, December 1953.  Submerged speed on an electric motor and batteries was a remarkable 33 knots.  Nuclear propulsion would arrive two years later.  The combination of a sleek hull and nuclear propulsion would have to wait for the arrival of the Skipjack class in 1959

The experimental teardrop-shaped Albacore also begat a class of three Diesel-Electric boats called the Barbel Class.  These vessels, which also use a teardrop hull, look nearly identical to modern nuclear submarines.

Below, a Barbel Class submarine, the diesel-powered USS Blueback (SS-581) moored in Portland, Oregon 2004

The Skipjack class is what I would consider a late first-generation nuclear submarine.  It incorporates many features shared by current submarines, such as the teardrop shaped hull, an attack center inside the hull instead of a conning tower inside the sail, and a powerful S5W reactor that became the mainstay of the US navy for decades.

The reason I don't consider Skipjack class ships second generation is because while they were very fast, they weren't particularly quiet. Nor were the hull or piping systems robust enough for these to be deep-diving ships.  You could also argue that they really were second-generation ships, because the hull was finally something not based on a diesel boat. 

Skipjack class boats were very nice looking.  Did I mention they were fast?  The Skipjack class pretty much standardized and finalized attack submarine shape and layout.  In all the decades since the Skipjack Class arrived the basic shape has not changed, although of course every aspect of the operating envelope has improved a great deal.

USS Skipjack (SSN-585) trying to perform a high speed surface run.  Skipjack class boats could run at 15 knots surfaced, 33 knots submerged.

But was the Skipjack Class the last first-generation nuclear submarine the US built?  Heck no!

The US built only one submarine that held two nuclear reactors.  That ship was the USS Triton (SSRN-589).  This ship was a "radar picket submarine".  The purpose of a radar picket submarine was to stay out ahead of an aircraft carrier group, and use radar to spot incoming threats before they got close to the carrier.  This essentially extended the radar detection range of the surface ship(s) in the carrier group.

Apparently, giving away the position of the most expensive submarine ever built by surfacing and sending out radar signals was OK, because that was how they were using her!  Different era, I guess...

USS Triton did not have a teardrop shaped hull, but she did have two reactors.  What she lacked in grace, she made up in punch - she achieved her speed through raw power.  Because she lacked a  teardrop shaped hull, she was slightly faster surfaced (30+knots) than submerged (27+knots).

She isn't very pretty.  Triton launch, August 1958.

Profile shot.  Still not pretty.   ...but two S4G reactors!

The Triton however, having two complete reactor and steam plants, was very reliable.  In 1960, on her shakedown cruise, she followed Magellan's course around the world - submerged the entire time.

The purpose of needing a "radar picket submarine" ended with the introduction of carrier-based early-warning aircraft, and so Triton was converted into an attack submarine.  She lasted about more 10 years in a Navy composed of ships that were increasingly faster, quieter, and less complex - at least from a propulsion and prototype perspective.

There was still another first-generation nuclear submarine.  USS Halibut (SSGN-587), the first US and only purpose-built nuclear-powered guided missile submarine.  With the exception of Halibut, the US Navy did not field nuclear powered guided missile boats until very recently.  The US Navy has retro-fitted four Ohio Class ballistic missile submarines (SSBNs) for cruise missile duty (SSGNs). 

Below, Halibut launching a Regulus guided nuclear missile.

Halibut steaming on the surface.

I discussed Halibut and her diesel-electric cousins in this post, so I won't go into it more, other than to say she was the last unusual design before everything became quite standardized.

Afterward were the Thresher/Permit class (14 boats), the Sturgeon Class (37 boats), and Los Angeles Class (62 boats).  The Thresher/Permit Class had one variant, and the Sturgeon Class had two variants.  You can review them at the links provided.  Interesting variations...