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Saturday, December 06, 2014

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 so went the cold war propaganda...

In fact, the hull and superstructure vibrated so badly that Nautilus sonar became useless at over 4 knots, so the lessons learned were incorporated into later designs.

While Nautilus was a ground-breaking and breathtaking ship, in many ways she was a simple old-school Tang-Class diesel submarine with a pressurized water reactor instead of diesel generators and massive storage batteries.  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 a Tang-Class submarine with a nuclear reactor instead of the diesel-electric components.  She was commissioned in March of 1957. This ship used a very advanced reactor propulsion system that turned out to be overly complex and maintenance intensive.

The primary coolant system used on Seawolf was the S2G liquid-sodium cooled reactor.  By using liquid sodium, the reactor could be operated at higher temperatures and lower pressures.  Also because it carried more heat, steam could be superheated, raising efficiency further.  The system operated at only 15 psig, so it was quite light.  However...

The superheaters suffered from poor tubesheet welds and leaked steam into the liquid sodium coolant, a problem that caused formation of sodium hydroxide (a caustic) and hydrogen gas (explosive when mixed with air).  Any minor breakdown that might result in the sodium coolant dropping below the melting point would cause the system to freeze up, a maintenance nightmare.

In 1960 Seawolf 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 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.

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.

Importantly for the new nuclear-powered submarines, a single prototype diesel-electric submarine had been testing the advantages of streamlining for optimum underwater performance, and this was the "Auxiliary Submarine" AGSS Albacore .  She was the result of wind-tunnel testing and revolutionized design by using a teardrop shaped hull, thereby 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 power would have to wait for the Skipjack class to arrive in 1959

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

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 they deep-diving.  The were very nice looking.  Did I mention they were fast?  One thing the Skipjack class accomplished was to standardize the attack submarine shape and layout.  In all the decades since Skipjacks, submarine fundamental design has not changed, although of course everything 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 Skipjack the last first-generation class of nuclear submarine the US built?  Heck no!

The US submarine fleet had only one ship that had two reactors, and that was the USS Triton (SSRN-589).  This ship was a "radar picket submarine", meaning she was to stay out ahead of an aircraft carrier group and use radar to spot incoming threats before they got close to the carrier - essentially extending the radar detection range of the surface ship(s).  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.  She achieved her speed through raw power.  Lacking a the teardrop shaped hull, she was 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 notion of a radar picket submarine ended with the introduction of carrier-based early-warning aircraft, and so Triton was converted into an attack submarine.  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.
She lasted about more 10 years in a navy composed of faster, quieter and cheaper to refuel ships.

USS Halibut (SSGN-587), the first and only US nuclear powered guided missile submarine.  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 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.  I may discuss them in the future!  Interesting variations, those...

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