Torpedo Problems - A Review Of The Sequence Of Events

The first problem that was noticed was premature explosions: the torpedoes detonated too far away from their targets. This was quickly attributed to defective magnetic influence exploders. But when the magnetic influence feature of the exploder was disconnected (against BuOrd’s directives), relying solely on the contact exploder, the “miss” situation did not improve. Further use of the torpedo (resulting in more misses) suggested that the torpedo was running too deep (considerably deeper than the depth settings) and was passing harmlessly under the target. During this time USS SARGO fired 13 torpedoes at 6 different targets with no results (even after dismantling the magnetic influence feature of the Mark 6 Exploder).

When the depth error was finally appreciated and the submarine commanders were instructed to subtract 10 feet from the depth settings (while keeping the magnetic influence feature active), the problem of premature explosions became more evident. This led to the July 1943 order by Admiral Nimitz to officially deactivate the magnetic influence feature on all torpedoes aboard Pacific Fleet submarines.

The Southwest Pacific Fleet submarines (under the command of one of the principle advocates and originators of the Mark 6) finally deactivated the device on their torpedoes in January 1944. The southern hemisphere is far from an ideal magnetic environment for a device essentially designed to work in the earth's magnetic field found in Narragansett Bay, Rhode Island. Still, the productivity of the submarines did not increase, instead a new problem surfaced: duds

This new problem of duds occurred when a torpedo hit the target but failed to explode on contact. The outstanding example of this is represented by the experience of USS TINOSA (which had the magnetic exploder deactivated on all 16 of its torpedoes). The commander spotted a large tanker, the TONAN MARU No. 3, (a 19,000 ton converted whale factory ship) doing 13 knots and proceeded to pump 15 torpedoes into her. Of the 13 torpedoes that hit the tanker, only one detonated (some sources say two detonated). His position was considered perfect, exactly 90o from the target at a range of just 875 yards. The commander took the last torpedo home in disgust while a Japanese tug towed the crippled tanker to Truk where her cargo was salvaged. This incident occurred on 24 July 1943, the very day the magnetic influence feature was deactivated from torpedoes aboard ships based at Pearl Harbor. (Note that a large water splash will result from a dud due to the air flask bursting and could be mistaken for a high order detonation of the warhead.)

It wasn’t until Oct. 1943 that the problems with the Mark 14 Torpedo were resolved and the submarine service began to show an improved performance record.

The Three Main Torpedo Problem Areas

Torpedo problems were reported early in the war by the submarine commanders, but were usually met with disbelief. BuOrd and SubPac staff officers placed the blame for the low number of sinkings everywhere but on the torpedo. They blamed the captain’s cautious tactics, a bad case of nerves, incompetence, improper handling and/or operating of the weapon, crew inexperience, and poor torpedo maintenance. BuOrd, with its vested interest in the exploder, did not believe the torpedo problem reports, and in general resisted the need to do any comprehensive testing and make changes. Toward the end of the first year of World War II nearly a third of the submarine commanders were replaced for poor performance or unsuitability. Many were criticized for lack of aggressiveness and unproductive patrols.

But, the torpedo problems were very real and can be broken down into three separate areas: (a) the depth-control mechanism, (b) the new magnetic influence feature, and (c) its backup contact exploder. The last two problem areas are buried in the new Mark 6 Exploder. These problems were not uncovered all at once, so as soon as one problem was solved the next one showed up.

The Depth Problem

Two separate issues contributed to make the Mark 14 Torpedo run deeper than the torpedo set depth.

1. The hydrostatic device which measured the surrounding sea water pressure (used to find depth) was not placed on the torpedo in a location where it could faithfully measure the sea water pressure. It was place well aft, in the "afterbody", near the diving control surfaces (diving planes) which it controlled over the skin of the torpedo at that location, the pressure was actually less than the pressure of the sea water just a few inches away from the skin of the torpedo (Bernoulli’s principle). So, while the torpedo was running, it always registered a lesser pressure, which produced an inaccurate depth measurement (a depth shallower than the actual depth of the torpedo). This inaccurate depth was transmitted to the depth control surfaces causing the torpedo to dive to a deeper depth than the depth set before launch.

2. The TNT (later Torpex) filled warhead was heavier than the exercise section used during torpedo testing on the tracking range. And, at the request of the Fleet, it got increasingly heavier as BuOrd added more explosives; bringing the total up from 507 pounds of TNT to 668 pounds of Torpex by the fall of 1942. This effect exaggerated the difference between the warhead weight and the exercise section weight. This problem originated early in the development of the Mark 14 Torpedo by the need to test the torpedo without any explosive charge in the warhead; instead water was substituted for the explosive charge during in-water runs on the Newport tracking range (to ensure torpedo recovery). At the end of the run the water was expelled and the torpedo surfaced for recovery. Before the war the exercise sections approximately weighed as much as the warheads, but as more explosive charge was added to the warhead during the war the weight difference was magnified. Also contributing to the depth sensor problems was the fact that the sensor was calibrated using this lighter weight exercise section. Since the lighter weight exercise section produced a torpedo of less density than an actual warshot torpedo, an inaccurate value for torpedo weight and trim was provided to the Fleet. During actual wartime service, with the heavier weight warhead, the torpedo ran deeper than it did on the Newport tracking range (but the range couldn't measure depth anyway).

Almost every time the Fleet reported an error in the running depth of the Mark 14 Torpedo BuOrd would quickly send out a representative to investigate. But all too often the report was to place the fault everywhere but on the torpedo (inadequate maintenance, improper handling, etc.).

The operating forces could not tolerate this error in depth and began a series of test programs on their own. One such test was a controlled depth test conducted in June 1942 in the waters south of Fremantle, Western Australia. USS SKIPJACK fired three exercise torpedoes at a large 500 foot long fishing net placed at a distance of 850 yards from the submarine. The torpedoes ran an average of 11 feet deeper than the set depth. In another demonstration at the Albany, Western Australia test site involving USS SAURY, the three torpedoes again ran 11 feet deeper than set.

BuOrd was unimpressed, until Admiral King (the Chief of Naval Operations) ordered the bureau to run proper tests. A series of tests were conducted at the Newport tracking range in Narragansett Bay which convinced BuOrd to admit, in August 1942, that the new Mark 14 Torpedo ran 10 feet deeper than set (a new depth control mechanism was later introduced).

More Mark 14 Torpedo

The Silent Service WWII USN Mark 14 Submarine Torpedo. Part 1 [# 120]
The Silent Service WWII USN Mark 14 Submarine Torpedo. Part 2 [# 121]
The Silent Service WWII USN Mark 14 Submarine Torpedo. Part 3 [# 122]
The Silent Service WWII USN Mark 14 Submarine Torpedo. Part 4 [# 123]
The Silent Service WWII USN Mark 14 Submarine Torpedo. Part 5 [# 124]