Examination of the wreck, first by Mizar’s towed cameras, then in 1969 by the bathyscaphe Trieste IIshowed no sign of serious hull damage in the region of the torpedo room, which would be expected if a warhead had detonated inside. Yet the photos did show that the torpedo room loading and escape hatches had been sprung open. This was a perplexing paradox in Craven’s theory. Try as he might, he could not explain the contradiction.
The Navy Board of Inquiry’s final report suggested several possible reasons for the loss, but nearly all involved equipment failure, not the explosion of a weapon. That was where the matter ended, at least for the next 25 years. The families of the dead crew were left in limbo as to what had really happened.
The Chicago Tribune published a story in 1993 that the Navy had at last released the official report and videos of the wreck on the 25th anniversary of the sinking. Craven, then 69 and retired, was named as being instrumental in the search for the sub. It also mentioned his theory about the hot run torpedo. The article came to the attention of someone Craven had never met.
Charles Thorne had been the technical director of the Weapons Quality Engineering Center at the Naval Torpedo Station at Keyport, Washington, in 1968. Thorne, who was retired, had read the Tribune story and decided that he had to talk to Craven. The two men found that each was sure that Scorpionwas lost from an exploding torpedo. But unlike Craven, Thorne had information that shed an entirely new light on the mystery.
The Mark 37 antisubmarine weapon acoustic torpedo, built by Westinghouse, had entered service in 1956. It was a marvel of underwater weapons technology; it weighed 1,400 pounds and was just over 11 feet long. It carried 330 pounds of HDX high-explosive in the warhead. Designed to sink enemy subs by blasting a hole in the tough outer hull, the Mark 37 was a deadly and efficient weapon.
The silver-zinc batteries were about five feet long and separated from the 330-pound warhead by a half-inch-thick partition. But there was a hidden flaw in the design that only became apparent in 1966 when the Mark 37 was already in service. Between the battery and the power cell was a tiny foil diaphragm only 1/7000th of an inch thick. This was supposed to rupture when pressure was applied by the ejection of the weapon from a torpedo tube, causing electrolytes in the power cell to fully activate the battery, which then started the motor. But this tiny part was very fragile and could easily be ruptured by a shock or vibration. The testing lab said the battery had no margin for safety and recommended the design be changed. Under pressure from the submarine fleet, the OSC refused to do so.
In April 1968 even as Scorpion was preparing to leave the Mediterranean and return home, Thorne’s team had been testing the torpedoes and key components. Tests included subjecting them to shock, heat, vibration, and other conditions that might happen aboard a submarine. They subjected one of the 250-pound batteries to strong and sustained vibration. It was mounted on a table, and just as the technicians left the room, a huge explosion made the walls shake. They reentered to find the battery engulfed in blue-green flames that shot nearly to the ceiling. Shrapnel and smoking acid were sprayed all over the room. Only after determined effort did they manage to disconnect the burning unit and extinguish the flames. The battery had been distorted and melted from the intense heat.
A written alert was immediately sent to the fleet under Thorne’s signature. The alert stated that all of the submarines in the fleet that carried Mark 37s with the flawed batteries should disconnect them immediately pending replacement. Even after the test, the OSC continued to insist that it was impossible for a battery explosion to set off a warhead. In fact, an OSC representative berated Thorne for suggesting such a thing in the alert.
The main problem the Navy faced was expediency versus caution. The submarine force needed torpedoes, and the manufacturers were hard pressed to produce the required numbers. As a result, the OSC was rushing into service torpedoes containing components that had not been fully tested. One company, subcontracted to produce the batteries, failed to manufacture even one that passed the quality control tests. But the Navy was in a bind. The service allowed that company to ship more than 200 batteries to the fleet. The unit that exploded in the testing lab was one of these. Upon hearing that Scorpionhad sailed with at least one torpedo that contained a defective battery, Thorne became convinced that this was the key to the disaster. Scorpion had been sent to sea with torpedoes that were vulnerable to vibration, and the submarine had a history of serious vibration problems.
When they talked in 1993 Thorne was astounded to find that Craven had not known of the alert. He had assumed that Craven was aware of the flaws in the battery. But as things turned out, Craven was not the only one involved who had not known that the faulty batteries could overheat and explode. The board of inquiry apparently also had not been made aware of this crucial fact. After his talk with Thorne, Craven reasoned that the tiny diaphragm could easily rupture from shock or vibration. If this was the case, the foil might only partially rupture, allowing a miniscule amount of electrolyte to leak into the power cells, which was not enough to start the motor, but could cause overheating and sparking. This is what happened in the lab. But right up to the moment of the explosion there had been no outward indication that anything was amiss. If this had happened in a torpedo on board a sub, the first hint of a problem would be intense heat rapidly building up in the battery compartment until the paint on the body blistered and seared. Only then would a crew member realize the danger and call the control room to report a hot run or hot torpedo. They might have had only seconds to move the weapon into a tube to be ejected into the sea. After his talk with Thorne, Craven was sure that Scorpion did not have those precious few seconds.
Did an overheating battery sink Scorpion and did a warhead cook off? This bears some consideration. The wreck shows that the torpedo loading hatches and escape hatches leading to Scorpion’s torpedo room are open. If a 330-pound HDX warhead had detonated, it would likely have caused sympathetic explosions of nearby torpedoes. If that had been the case, the entire forward section of the submarine would have been torn apart. The wreckage, while severe, does not show any external distortion from massive internal explosions. What is more, unlike virtually every other compartment, the torpedo room was not crushed by external pressure. This is highly significant. It means that the torpedo room was probably already flooded when the submarine sank.
But it would be folly to totally rule out a warhead explosion. In normal operations, when 330 pounds of HDX detonates upon impact with an enemy ship, the force is directed straight ahead to penetrate the hull. But if a battery fire had cooked off a warhead, the resulting blast would be undirected in what is known as a low-order explosion. This might not cause other warheads to blow up, but would very likely blow off the hatches, flooding the torpedo room and dooming the submarine even if all the watertight doors had been sealed. The rest of the crew would have watched in stunned horror as the bulkheads started to wrinkle and bend as the steel was subjected to thousands of pounds of pressure per inch. One by one the compartments, starting with the bow and stern, would be shoved into the main hull, tearing the ship apart. The crew would have been immolated in microseconds as the air was compacted into incandescence. The entire sinking took three minutes and 12 seconds from the first explosion to the final collapse. The result was a long fall and immediate death for 99 American sailors. To this day the OSC has never acknowledged that Scorpion’s loss was caused by an internal torpedo explosion or even that she had carried one of the flawed batteries. But one year after the loss, OSC did order a redesign of the battery for the next generation of torpedoes. This year marked the 50th anniversary of Scorpion’s loss without a solid answer for the crew’s families.
(This article was originally published on May 11, 2019 and is being republished due to reader interest.) This article originally appeared on the Warfare History Network.
This article originally appeared on the Warfare History Network.
Image: Wikimedia Commons