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594 Tough…


On 10 April, 1963, the USS Thresher SSN-593, accompanied by the submarine rescue ship USS Skylark ASR-20, was nearly 200 nautical miles east of Cape Cod conducting post overhaul trials.  Aboard were 129 men, which included “riders” from the Portsmouth Naval Yard (PNY), along to oversee, adjust, or fix any of the newly installed or refurbished equipment.  A lot was riding on Thresher’s performance that morning including the direction of the nuclear submarine fleet.  Thresher was the first of a whole new breed nuclear submarine known as a “hunter/killer, fast attack.”  While the USS Nautilus (SSN-571) ushered in nuclear propulsion aboard submarines, and the four-boat Skate class (SSN-578) had proven nuclear propulsion a viability for repeatable production, then the six Skipjacks (SSN-585) advanced speed and performance with a more efficient hull design, Thresher leaped submarine technology beyond these past achievements to a whole new paradigm. Thresher was born out of a 1956 Cold War study (Project Nobska, or Nobska Committee, or Nobska Study) developed by the leading scientist, engineers, and naval officers of the time, who analyzed and compiled criteria on the expected threats facing submarines in the coming decades, and put forth recommendations as to best counter them. Among the several recommendations, that became part of Thresher, was:

(1) A layout optimized for the newest sonar systems, specifically configured for hunting other submarines.

(2) A robustness and versatility for handling a mix of the latest weapons, as well as adaptability for future weapons still in conceptual stages.

(3) A hull profile optimized for performance and speed, which became an elongated adaptation of the new “teardrop” shape with single propellor, first successfully employed in the experimental Albacore (AGSS-569), then utilized in production with the diesel/electric Barbel class (SS-580) and the nuclear powered Skipjacks.  This gave Thresher unprecedented maneuverability and speeds, unofficially listed as 29 to 30 knots, which was comparable to those achieved by the fastest boats, the Skipjacks (unofficially listed as 32 to 33 knots).

(4) The hull was to be constructed of the strongest materials then available, so a new grade of low carbon/high yield steel, known as HY-80 (per MIL-S-16216K Yield Strength: 80 ksi/Ultimate Tensile Strength: approximately 130-145 ksi [when specified]) was employed.  This new grade gave the Thresher an unprecedented operational depth of 1,300 feet, at a time when the average diving depth for new construction was rated at 750 to 800 feet.

(5) But the greatest effect of the study, and Thresher’s most enduring feature, was the level of detail placed on stealth and silencing; simply put noise is the enemy of the submariner.  Noise not only gives away a submarine’s position, it also robs a boat of clear sonar reception when stalking an enemy. In the Thresher, all major propulsion machinery (reduction gearing, pumps, compressors, turbines, etc.) was isolated from the hull on a large shock absorbing platform, known as a “raft.” She received a specially configured seven-bladed propeller to reduce the effects of cavitation and disturbance when cutting through her own flow stream.  Decks and bulkheads, where applicable, were fitted with sound absorbing materials.  Even bolt joints, were fitted with rubber washers.

The results incorporated, made Thresher the most advanced and lethal submarine ever constructed to that time. Yet for all her technical innovations, her first year-and-a-half in commission had not been as successful as the Navy had hoped. She had been plagued with several major issues, and started to gain a reputation as an unlucky boat. And, with the addition three sister boats already in commission (Permit, Plunger, and Barb), plus more building, the Navy was placing a lot in the just-completed overhaul at PNY. So, at around 0630 local time Thresher began her decent for deep submergence testing. She maintained communications with Skylark via an underwater telephone system known as ”Gertrude.”  Thresher would descend in 100-foot increments, stop, and check critical systems for integrity before continuing deeper.  As Thresher neared her test depth, Skylark began to receive garbled responses, but enough got through to indicate the submarine was in trouble and unable to return to the surface, despite an attempt at an emergency-blow of her main ballast tanks. Soon there was only silence on Gertrude, and with no further responses from Thresher, the crew on Skylark knew the submarine was lost with all hands.

Thresher’s loss stunned the Navy like none prior, and the submarine community, in particular, was rocked hard. Many began to question the validity of the Thresher’s design, and crews serving aboard her sister boats could not help but wonder if they too were serving on death traps. All post-war designs were immediately relegated to depths no greater than 600 feet, while an official inquiry was convened. Over the next few months, everything pertaining to Thresher underwent extreme scrutiny, and the inquiry was able to piece together a rather detailed scenario of the events, as well as identify the systems most likely to have suffered the casualties necessary to have led to her demise. The details of Thresher’s loss are beyond the scope of this narrative, but drastic adjustments to the engineering, quality control, and manufacturing procedures of submarines went into effect.  New and improved safety features were incorporated into the Thresher’s design and added to boats still on the building-ways, or retrofitted to existing boats during periodic overhauls. These corrections as a whole became known as the SUBSAFE program, and are still an integral part of submarine design and manufacture to this day.

But, just as critical as determining and correcting the causes of Thresher’s loss, is the fact that the US Navy did not give up on her design or concept. In fact, just the opposite, as mentioned the class continued in production with major improvements, for a total thirteen additional boats of her class. But not only did the class continue, the Navy evolved Thresher’s design into an improved class that would number 37 boats, and become the ”workhorses” of the submarine fleet for the duration of the Cold War; that class was the vaunted USS Sturgeon SSN-637 class. And when the Navy started with a new design that would become the Los Angeles SSN-688 class, the basic layout and design concepts introduced in Thresher were continued.  The design proved successful enough, that even the current Seawolf SSN-21 and Virginia SSN-774 classes are built to much the same concepts that first spawned Thresher.

As for the thirteen remaining boats of the Thresher class, they to went on to have successful careers, that spanned more than three decades right into the immediate post Cold War years, with the last boat not decommissioning until 1996. It is also noted that as the Thresher’s were being paid off, several of the much younger Los Angeles class submarines were being retired within just a few years, giving testimony to the longevity of the Thresher class.

Yet as durable, rugged, viable as the class would prove, in 1963 the Thresher’s loss still left a stigma hanging over the class that had to be addressed. The first immediate change, outside of the inquiry, was to minimize the humiliation of losing the class leader (the Cold War was as much about propaganda, good or bad, as anything else that defined it).  By default the the second boat in the class, the USS Permit SSN-594, took on the moniker “class leader,” and henceforth the class was referred to as the “Permit class” or “594 class”. However, even with a name change, and design improvements added, these thirteen boats still held a reputation as hard handlers, requiring care and concentration to control.  Their characteristics, of speed and maneuverability, in conjunction with the location of their control surfaces relative to their length, meant they could be ”tough to handle, ” especially when compared to the previous Skipjacks, or the follow-on Sturgeon and Los Angeles classes. The sailors who served aboard them, either loved them or hated them for this trait, but the fact that they endured as front-line, first rate fast attack boats right up through their retirement, gave real meaning to the phrase ”594 tough.” This phrase symbolized both a respect or hatred for a class of submarines, that like a wild animal, if not tamed could bite the men who sailed in them, just as easily as their Soviet prey; indeed as mentioned one crew paid the ultimate sacrifice. Nevertheless, the phrase also symbolizes the type of men who went to sea in these boats and carried out hard assignments that very few in the US Military could handle. So whether referring submarine or sailor, they were 594 TOUGH.

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