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The Evolution of USN Submarine Launched Weapons - Part I - Torpedoes

August 27, 2020

Civil War Through the Cold War Era
Just as submarines have evolved from the earliest days of the Alligator and the USS Holland so too have their weaponry. The word torpedo is rooted in the name of electric sea rays whose name comes from the Latin torpere meaning "to be stiff or numb". In naval usage, the American Robert Fulton introduced the name to refer to a towed gunpowder charge deployed by his French submarine Nautilus, first tested in 1800, to demonstrate that it was capable of sinking warships.
The first reasonably successful but rudimentary underwater weapon termed a spar torpedo was invented by engineer E. C. Singer for the Confederate States of America during the Civil War that had an explosive charge mounted on a wood
en spar extending out from the attacking ship and was detonated by a trigger mechanism actuated by means of a cord attached to the attacking vessel. Upon ramming its target and embedding the barbed torpedo into its hull it then backed off until the limit of the trigger cord was reached and the torpedo detonated.  It was a spar torpedo that the CSS Hunley was employing when it attacked the Union screw sloop USS Housatonic on February 17, 1864 and sank due to its malfunction. Regardless, spar torpedoes remained the submarine weapon of choice until 1866 when British engineer Robert Whitehead invented the first operational self-propelled modern torpedo. Soon after, French and German inventions followed suit and the term torpedo came to describe self-propelled projectiles that traveled under or on the water surface.
The initial trials of the  “Whitehead torpedo” failed because it failed to maintain a steady course and depth however he overcame those difficulties utilizing a mechanism consisting of a hydrostatic type valve and pendulum that activated the torpedo's hydroplanes to adjust automatically in order to maintain a preset depth.
Subsequently Whitehead opened two factories, one near Portland Harbour England and the other at St Tropez on the French Rivera to manufacture and export torpedoes to Brazil, Holland, Turkey and Greece.  And by World War I Whitehead maintained a monopoly on torpedo production worldwide.
Then in 1915 the United States deployed the Mark 10 torpedo that was derived from the existing Mark 9 aircraft torpedo and converted for submarine application. It was succeeded by the problematic Mark 14 torpedo, however stockpiles of Mark 10 Mod 3 torpedoes saw extensive action during the first part of World War II.  
 Development of
the Mark 6 exploder for the Mark 14 torpedo warhead had started at the Naval Torpedo Station (NTS) Newport in 1922. And because surface ships’ armor was evolving with innovations such as torpedo belts and torpedo blisters or bulges, torpedoes required larger warheads to be effective against  the thicker hulls.  So an alternative was be to utilize a more compact warhead that was designed to explode beneath the keel where there wasn’t any armor and break the keel essentially splitting the target in half. And, that strategy resulted in the development of the sophisticated Mark 6 magnetic influence exploder.
 Torpedoes were expensive in 1931 therefore the development of the Mark 13, Mark 14 and Mark 15 torpedoes was done frugally and the Navy resisted engaging in live fire tests that would destroy torpedoes and target ships. Consequently, engineers relied on their judgment rather than test results that sadly were sometimes erroneous and so the exploder reliability was irregular at best. Too,
the frugal depression-era peacetime testing of both the torpedo and its exploder mechanism was woefully inadequate and so had not revealed the many  design flaws until they came to light as torpedo after torpedo either missed the target completely, prematurely exploded, or struck targets with textbook hits sometimes with an audible clang, yet failed to detonate.
However, in spite of its inadequacies the MK-14 remained the predominate weapon on USN submarines through the 1950s and were still in use into the early 70s when a typical Attack boat weapons load consisted of the MK-14- Mod-5, the newer, MK-16- Mod-8 anti-ship torpedoes, the Mk-37-Mod-2 wire guided anti-submarine torpedo, the MK-45 Astor nuclear tipped anti-submarine torpedo, and the U

UM-44 Nuclear tipped Subroc Missile. And, were all eventually replaced with just two weapons, the Mk-48 ADCAP torpedo and Cruise missiles.
The 1960s were an interim era in USN undersea weapons history in that it was a bridge between the deployment of WWII vintage torpedoes and the modern torpedoes and missiles to come. And one that I was personally familiar with because I served as a submarine Torpedoman aboard a 637 class Fast Attack submarine from 1969 to 1973. The 14s remained problematic and when I was assigned as a Torpedoman aboard USS Bluefish SSN-675 I became involved in an event during a 68-day submerged recon patrol into Soviet Territorial waters when we had four fully armed torpedoes loaded in our tubes for self-defense if necessary. They were two MK-37 Mod 2s and two Mk-14 mod 5s. Three weeks into the patrol I observed a repeated and unusual buildup of air pressure inside tube #2 with a 14 loaded. Eventually, after isolating the tube from all outside air supplies and repeatedly venting off the pressure over a three watch rotation period I was able to deduce that the fish loaded inside had a leaking air flask and therefore was in danger of starting up prematurely on its own resulting in a dangerous situation called a hot run. Had that occurred it could have resulted in an explosion of the turbine due to over spinning in a dry tube and/or detonating the attached warhead. Therefore, upon concurring with my weapons officer and on my recommendation our Captain ordered that we pull the “fish” from the tube. Then, as two other TM shipmates worked on removing the control valve from the torpedo body in order to render the torpedo inoperable and negate the hot run, I assisted by another torpedoman, disarmed the warhead. Fortunately, we all succeeded in time and the twofold emergency was negated.
The MK-14s were each accompanied with a pamphlet type log book that listed all its prior duty stations all the way back to WWII. And, I would thumb through them and see that I had fish on board that survived some of the big battles of the war. Also, their inner workings although Rube Goldberg like in their operation compared to modern technology, were magnificent works of American craftmanship, all copper, brass and polished steel. And, their warhead casings were made of bronze.
The Mark 16 torpedo was a redesign of the  Mark 14 torpedo to incorporate war-tested improvements for use in fleet submarines, and it was considered the USNs standard anti-shipping torpedo for twenty years during the Cold War. The high-test hydrogen peroxide propelled, 21-inch torpedo was 20 feet 6 inches long and weighed 2.0 short tons with a warhead containing 1,260 pounds of TPX explosive and was the most powerful conventional submarine torpedo ever used by any Navy; It could be set for straight or pattern-running. We carried the Mk-16 Mod-8 that had a sight glass on its body that had to be monitored for bubble activity to ensure that the Hydrogen Peroxide remained stable.
The MK-37 wire guided anti-submarine torpedo was a battery powered electric propulsion weapon that entered service in the early 1950s with over 3,300 produced and was phased out of service during the 1970s, and the stockpiles were sold to foreign navies.  Its electric propulsion dictated that the weapon “swim” smoothly out of the launch tube rather than being impulsed out therefore significantly reducing its acoustic launch signature. Its guidance was threefold and first accomplished through gyroscopic control during the initial part of its trajectory, then a passive sonar homing system, and for the last 700 yards by Doppler-enabled active sonar homing with magneto-strictive transducers. The wire-guidance was through a wire reel mounted inside the torpedo tube and connected to the firing submarine’s fire control system. The fish ran through the water at slow speed searching for the target with passive sonar then upon acquisition it shifted to high speed and active sonar pinging until contact and detonation. If it lost target acquisition it would then shift back to slow speed and go into a diving screw like search pattern in an attempt to reacquire the evading submarine. It was comparable to an underwater heat seeking missile but it locked on to sound instead. For much of the Cold War the Mark 37 was a primary U.S. submarine-launched ASW torpedo and was replaced by the Mark 48 starting in 1972. The remaining inventory was then rebuilt and sold to several countries, including Israel, as the NT-37C.   
The Mk-37 was a troublesome weapon too and was suspect in the sinking of USS Scorpion SSN-589 in 1968 because its Mk-46 silver-zinc batteries were prone to overheating, occasionally igniting, exploding or initiating a hot run of the torpedo. Because Scorpion is lying on the ocean floor nearly reversed from its last reported course for home it’s thought that the Captain may have been attempting to turn the ship and therefore the torpedo 180 degrees causing the anti-circling device to actuate and shut down the torpedo. While I was on Bluefish a directive was sent out that instructed that in the event of an overheating battery or a hot run to load the fish into a tube and flood it down in order to cool down the battery section. And, under no circumstances to eject it because it’s unknown what target coordinates were set in making it possible to circle back and hit the firing submarine.
Although not a torpedo the UUM-44 SUBROC (SUBmarine ROCket) was a submarine torpedo tube launched rocket anti-submarine weapon that carried a 250 kiloton thermonuclear warhead configured as a nuclear depth bomb. It was impulse launched from a standard 21-inch diameter torpedo tube, then post launch it acquired a 45 degree up-angle and the solid fuel rocket motor fired. Next SUBROC broke the ocean surface and the missile proceeded to apogee, initiated rocket motor separation, and the nuclear depth charge descended to its target destination following a predetermined ballistic trajectory 25 miles down-range where the 250 kiloton W55 nuclear depth bomb reentered the sea and actuated by pressure switch detonated near its target. A direct hit was unnecessary as it virtually vaporized five square miles of ocean above and below. Subroc was my personal favorite of our weapons because it was so bad assed and it looked it too.
 In order to prep the weapon for launch after removing the fin guards we fitted a break away shock mitigating nose cone on the warhead to protect it during water entry. Next, we installed a battery into the warhead that initiated the primary explosive detonation, and lastly, we installed a radioactive gas filled canister that facilitated fusion and the resultant nuclear detonation. The canister contained a radioactive gas that was was colorless, odorless and tasteless and would kill the entire crew quickly should it leak out undetected into the boat’s atmosphere. Accordingly, there were two alarmed atmosphere monitoring devices to specifically detect that gas, one located forward and one installed aft on the submarine to warn the crew to don emergency breathing gear quickly. Once Subroc was loaded into the tube we connected three “umbilical cords” that allowed the missile to communicate with our MK-113 fire control system. Then when the firing button was pressed in the control room it was merely a permission for the rocket to fire because it sat in the tube going through its pre-launch check downs until it was ready to go and when completed after a few minutes it launched itself and was away to the target. And that was pretty remarkable to a 20-year-old kid back 50 years ago as were most things related to being a submariner.
SUBROC's tactical use was as a long-range attack weapon against time-urgent submarine targets that could not be attacked with any other weapon without betraying the position of the launching submarine, or where the target was too distant to be attacked quickly with a conventional submarine launched torpedo. An added advantage was that SUBROC's approach to the target was undetectable by the target in time to take evasive action, although the kill radius would make evasive maneuvers unrealistic.  
SUBROC production ended in 1968, was never used in combat, and all 285 W55 warheads were decommissioned in 1990 following the end of the Cold War. Because the nuclear warhead was an integral part of the weapon, SUBROC could not be exported to other navies.
The Mark 45 Astor anti-submarine torpedo was a 2400 lb. submarine-launched wire-guided nuclear torpedo deployed by the United States Navy for use against high-speed, deep-diving, enemy submarines that was was fitted with an 11 kiloton W34 nuclear warhead. The design was completed in 1960, and 600 torpedoes were built between 1963 and 1976 when ASTOR was replaced by the Mark 48 AD CAP torpedo.
The requirement for positive control of nuclear warheads meant that ASTOR could only be detonated by a deliberate signal from the firing submarine, which necessitated a wire link. Because of this, the torpedo was only fitted with wire guidance systems and had no homing capability. Production of ASTOR began in 1959 and it entered service soon after with 600 torpedoes being built by 1976 when the torpedo was replaced by the Mark 48 torpedo. The ASTORs were refitted with conventional warheads and sold to foreign navies as the Mark 45 Mod 1 Freedom Torpedo.
The MK-45 Astor had a kill range radius of 8 miles and its purpose was a last resort weapon to be used in a must kill situation against a Soviet FMB submarine that was poised to fire its missiles on allied population centers.  And, it’s been rumored that because of its extensive kill range it would destroy the firing ship as well as the target; essentially a suicide weapon. All I know is that each Attack submarine carried only one on patrols as if one was all we would ever need.

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