Sturgeon Class submarine variants

USS Sturgeon was the first of a new class boats which were the mainstay of the attack submarine fleet from the mid 1960s and well into the 1980s.  Here is what Wikipedia has to say about them:

Operators:	United States of America
Preceded by:	Thresher-class submarine
Succeeded by:	Los Angeles-class submarine
Built:	1963–1975
In commission:	1967–2004
Completed:	37
Retired:	37
General characteristics
Displacement:	3,640 long tons (3,698 t) surfaced 4,640 long tons (4,714 t) submerged
Length:	292 ft 3 in (89.08 m)
Beam:	31 ft 8 in (9.65 m)
Propulsion:	1 × S5W Pressurized water reactor 2 × 11.2 MW steam turbines 1 shaft
Speed:	15 knots (28 km/h; 17 mph) surfaced 26 knots (48 km/h; 30 mph) submerged
Range:	Unlimited, except by food supplies
Test depth:	1,320 ft (400 m)[1]
Complement:	107
Armament:	• 4 × 21 in (533 mm) amidship torpedo tubes with MK-48 and ADCAP torpedoes, plus 15 reloads, and 4Harpoon missiles or up to 8Tomahawk missiles, instead of equivalent of number of Torpedoes or Harpoons. In minelaying configuration: • Mark 67 Submarine Launched Mobile Mines and Mark 60 CAPTOR mines instead of torpedoes.

The Sturgeon class (sometimes called the 637 class, due to the hull number), was an incremental improvement over the Permit/Thresher class.  The improvements were primarily ones of size and auxiliary equipment. Depth and speed were similar, as was the propulsion plant.  The fairwater planes could be rotated to vertical for surfacing through ice, and the sail was enlarged to house additional intelligence-gathering equipment.

The last nine built were "stretch hulls", with an additional 10ft of length.  We called them "stretch limos", because they were about as luxurious as attack submarines ever got.  Of course to us, *any* 637 was the lap of luxury.

There were a couple of special operations boats in this class, notably the Parche, but also including Gurnard and Pintado.  These don't interest me much because even though they carried spooks around, they were still basically standard 637 designs.

Of interest to me, because they had unique power trains, were USS Narwhal (SSN-671) and USS Glenard P. Lipscomb (SSN-685).  These were truly unique ships from a propulsion standpoint, and that is what I find interesting.

USS Narwhal was launched in September 1967.  Her unusual S5G reactor used natural-circulation for cooling, thus eliminating a major source of noise that all other nuclear subs had to deal with: The primary coolant pumps.  She had primary coolant pumps available, but did not need to use them, unless high power levels were needed to increase ship speed.

Below, USS Narwhal, SSN-671.  A successful prototype.

Also eliminated on Narwhal were the reduction gears.  A multi-multi-multi-multi-stage, low-speed propulsion turbine was coupled directly to the propulsion shaft, completely eliminating the reduction gears (and their noise).  Rumor has it that this one-of-a-kind steam turbine was very problematic due to having an extremely long rotor that chronically suffered from bowing.  

Narwhal was also equipped with scoop induction for seawater, so that the forward motion of the ship would force seawater through her cooling systems, including the main condensers.  This allowed the main seawater pumps to be shut down, yet again reducing noise.  Narwhal was probably the quietest submarine built until the Ohio Class ballistic missile submarine arrived on the scene in 1981, carrying some of the features that Narwhal had successfully pioneered.

USS Glenard P. Lipscomb was launched in August 1973, and was a second attempt at turbo-electric propulsion, the first being the DC motor-driven USS Tullibee.



Unfortunately, Lipscomb (which instead used AC propulsion turbine generators) was larger and weighed vastly more than a standard Sturgeon Class boat, while still using the exact same power source (the S5W reactor). She was therefore quite slow (18 knots surfaced/23 submerged).  I have no idea if she was any quieter than a standard Sturgeon boat.  She had a relatively short life, being decommissioned in 1990, after just 17 years of active service.  Typical service life for a submarine is around 30 years.

EDIT:  A very knowledgeable commenter who served on the Lipscomb (SSN-685) has provided further information on the propulsion train of this unique vessel.  I'll quote him here.

SSN 685 propulsion was NOT AC ... it had two 1000 VDC propulsion turbine generators (PTG) each having twin armatures (2450 Amps max each Arm)... I can confirm as I had to change the brushes and clean the commutators... No reduction gears in these PTG - about 900 RPM max. The motor was direct coupled to the main shaft, 1000 VDC, twin armature, 4800 amps EACH, max. The boat was ultra quiet... had to wear a "pinger" to be allowed to play in NATO games. Carbon dust build-up and impregnation / insulation degradation where the demise (and deficient technical resources to correct these if other blogs are true). "

 So there ya go!