Lieutenant Dan Daspit, captain of the U.S. submarine Tinosa could not believe his luck. Framed neatly in the periscope eyepiece was a sitting duck. The 19,250-ton Japanese tanker Tonan Maru No. 3 was all alone, dead in the water. Tinosa was on her second war patrol, having left Midway atoll on July 7, 1943. For a week she had been prowling along the Japanese sea routes between Borneo and Truk. On the afternoon of July 24, Daspit spotted a thin trail of gray funnel smoke on the horizon. Remaining submerged, he set up a textbook approach and fired four Mark 14 torpedoes at the ship, which was making only 10 knots. Every one of his “fish” ran true. Thirty seconds later, the sonarman heard the repeated thumps of the torpedoes striking the hull, but no explosions. The tanker turned and increased speed.
Swearing, Daspit turned in pursuit. After a long nighttime chase, he was in position to try again. His torpedomen checked every fish to make sure it was working perfectly. Then, coming at the tanker from the starboard quarter, he fired two more torpedoes. Both hit and exploded. The muted rumble echoed through Tinosa’s hull. The crew cheered.
The Tonan Maru had been hit in the engine room and coasted to a stop. An experienced submarine commander, Daspit took his time approaching the ship’s port side. He would fire one torpedo at a time from 1,000 yards, aimed to strike the tanker’s hull at exactly 90 degrees. The 680 pounds of high-explosive Torpex would blast a huge hole in the hull. Two or three fish should send her to the bottom. The tanker could not run. Tinosawas going to hang the huge Tonan Maru’s scalp on her belt.
At 0930 hours, Tinosa fired her first torpedo. It ran straight and true. The wake was a long deadly white finger reaching out to touch the helpless ship. Then nothing happened. The torpedo had failed to explode. This was nothing new to the American submarine fleet, so Daspit fired again. No towering column of water erupted from the tanker’s hull. No crushing roar echoed through the deep.
Gritting his teeth in frustration, the sub’s skipper fired again. And again. Five, then six deadly Mark 14 torpedoes, the most advanced antiship weapons in the U.S. inventory failed to explode. The fifth one appeared to raise a tall plume of white water as a tinny “Phwyinng!” noise came through the hull. Number six broached and leaped after striking the enemy’s hull, then sank.
Then the tables turned. The Tonan Maru had radioed a distress call. A Japanese destroyer was coming with a bone in her teeth. Tinosa had to depart the area fast.
Daspit fired two more torpedoes at the tanker as his submarine turned away. The sonarman reported that both weapons seemed to hit and then stop.
As his sub raced eastward, Daspit wrote of the frustrating hunt in his log. “I find it hard to convince myself that I saw this.” He had no explanation for why the torpedoes failed to explode. Out of 15 Mark 14s fired, only two had detonated, and those had been fired from what was considered to be a very oblique angle. The others were so carefully set up as to be right out of the textbook. Yet not one had done its job.
Daspit headed directly back to Pearl Harbor doing what no American sub skipper ever wanted to do, returning with an “empty bag.” He was met at the Sub Pier by the new Commander, Submarines, Pacific (COMSUBPAC), Rear Admiral Charles Lockwood, a career submarine officer. Lockwood was a hard-driving, conscientious officer who had the reputation for giving full support to his squadrons, his boats, his commanders, and their crews. He took Daspit up to his office where the exasperated sub skipper related what had happened with the Tonan Maru.
Lockwood listened, nodding. He later wrote, “I expected a torrent of cuss words, damning me, the Bureau of Ordnance, the Newport Torpedo Station and the base torpedo shop. I couldn’t have blamed him. 19,000-ton tankers don’t grow on trees. I think Dan was so furious as to be practically speechless.”
But when the single torpedo Tinosa had brought back to Pearl was examined at the Submarine Base torpedo shop, it was found to be in perfect working order.
Lieutenant Commander Daspit’s report was the most recent and extreme case of what had been a growing problem within the U.S. submarine fleet since the beginning of the war. From the first patrols after the Commander-in-Chief U.S. Pacific Fleet (CINCPAC), Admiral Chester Nimitz, had ordered unrestricted submarine warfare on all Japanese shipping, submarine commanders had been complaining of torpedoes that failed to work properly. On December 14, one week after Pearl Harbor, the USS Seawolf encountered a Japanese freighter near the Philippines and fired eight torpedoes. Seven missed, one hit. And failed to explode.
So began the litany of problems with the Navy’s technical marvel. In the first months of war, American subs fired 97 torpedoes at enemy shipping. Only three ships were sunk. Some failed to explode, while others, even though aimed with care, seemed to miss or run under their target. Even worse, several had blown up before hitting the side of a Japanese ship.
Torpedoes were the first totally autonomous guided missile. The German Navy had sunk hundreds of Allied ships in World War I with torpedoes, and by 1925 the latest versions were highly complex machines. The Mark 14 was developed to replace the older, shorter Mark 10 that had been in service during and after World War I.
Designed primarily by engineers at the Navy Bureau of Ordnance (BuOrd), the Mark 14 was built at the Newport Torpedo Station (NTS) beginning in 1926. At 21 feet long, 21 inches in diameter, and weighing more than 3,000 pounds, the Mark 14s were large and expensive weapons. Powered by steam, they could run for 9,000 yards (5.1 miles) at 46 knots. They were extremely complex and required the most meticulous machine and assembly work. By 1940, they cost upward of $10,000 each, five times as much as a new automobile.
The most important component was the Mark 6 exploder, without which the torpedo would be useless. The certain way to sink a ship was to break its back at the keel. This often caused a ship to break in two. Obviously, this required a torpedo to explode under the hull. To this end BuOrd had designed the new exploder based on the successful British Duplex and German magnetic mine designs. Its most radical feature was the magnetic influence exploder, Project G53. It was a closely guarded secret, so much so that even though a maintenance and operating manual had been written it was never printed or distributed.
The magnetic exploder was triggered by the influence of a steel hull as it passed directly beneath a ship, where there was no armor. For this reason, the first Mark 14s carried a moderate warhead. BuOrd was under a tight budget and saw no reason to spend money on unnecessary testing. Only one test of the Mark 6 was conducted in May 1926. The target, ironically, was a derelict submarine. Two Mark 14s armed with the magnetic exploder were fired at the sub. One ran under the target and failed to detonate. The second one exploded and sank the sub. What was not being taken into account were variations in the Earth’s magnetic field. The Mark 6 was highly sensitive and too likely to detonate with even minor fluctuations. This was not considered a flaw, and in 1934 the Mark 6 was approved for fleet use.
No further testing was done. The U.S. submarine force went into combat with a torpedo with a 50 percent failure rate.
In 1939, the Navy demanded a larger warhead, and BuOrd authorized its increase to 680 pounds, enough to tear open the most sturdy hull. But, as events proved in the first year of the war, the magnetic exploder worked too well. Several sub skippers fired at their targets only to witness premature detonation well before the torpedo was close enough to do serious damage. Often the enemy ship suffered little more than dented plates that were easily repaired.
The Mark 6 also had a contact exploder, which consisted of a trigger, firing pin, and detonator. In essence it was not much different from a gun’s trigger, firing pin, and the primer in a cartridge. When the torpedo struck a ship’s hull, the head was rammed backward, driving the firing pin into the detonator over the warhead, causing it to explode. The contact exploder was intended to provide a backup in the event that the magnetic pistol failed to work. But since the warhead exploded even before contact with the hull, it was useless.