User Guide

the crew to relying on the magnetic detonator. This methodology disguised
several very serious flaws in the Mark 14 torpedo and the Mark 6 detonator
that were only revealed as each prior problem was solved. A 1943 Bureau of
Ships report on the circumstances of shipping sunk by U-boats also dis-
proved the keel damage theory. The report indicated that most damaged
ships that sank foundered from loss of stability rather than actual flooding.
Problems Arise
Submarines went to sea in 1941 and 1942 with a largely untried weapon, and
began reporting premature detonations and a number of missed shots. At
first, these problems were explained by the Bureau of Ordinance as “human
error.” The newly promoted Rear Admiral, Charles Lockwood made a priority
of getting to the bottom of the matter. After a number of reports of missed
shots, Admiral Lockwood had the submarines Skipjack and Saury test fire
Mark 14 torpedoes set for a depth of 10 feet at a net strung 850 yards away.
The first test, made by Skipjack on June 20, 1942 showed that torpedoes set
for 10 feet were punching through the net at depths between 18 and 25 feet.
Torpedoes set for zero depth ran down to 11 feet too deep.
These first tests were rejected by the Bureau of Ordinance, so a second set
of test shots were made by Saury on July 18. The results were the same.
Both Mark 10 and Mark 14 torpedoes would actually run as much as 10 feet
deeper than they were set. For the Mark 10 this was a serious problem,
since it actually needed to contact the enemy vessel to detonate.
Theoretically, this was less of a problem for the Mark 14, since the mag-
netic detonator should still cause an explosion when it entered the target’s
magnetic field. In practice this was not the case.
Detonator mechanisms were deactivated at the point of firing to prevent
them from exploding early while the torpedo “found its bearings.” The tor-
pedo traveled for approximately 450 yards after firing before the safeties
released and allowed the detonator, which was itself a small bomb, into
contact with the normally inert explosive in the warhead. At this point, sev-
eral mechanisms became active. Since a spread of torpedoes were fired
sequentially, they were equipped with a device to prevent the explosion of
one torpedo from triggering premature explosions in those nearby. This
anti-counter-mining device actually locked the magnetic exploder on some
deep-running torpedoes, preventing detonation.
Once the depth-setting problem was corrected, the next fault to appear was
the tendency to detonate prematurely. In this case, it was the magnetic deto-
nator that was found to be largely at fault. If the torpedo were running
shallow, it would encounter the ship’s magnetic field far enough away from
SILENT
HUNTER
52 TORPEDOES: Torpedo Types
The primary torpedo storage facility at Pearl Harbor endured the bombing
on 7 December 1941 largely unscathed. Unfortunately, 233 torpedoes were
destroyed by the 10 December bombing of Cavite Navy Yard in the
Philippines. Torpedo production at the war’s start was roughly 60 per month
from the torpedo manufacturing facilities at Newport, Rhode Island and
Alexandria, Virginia and reserves were only in the hundreds. Transportation
difficulties continued to make supply a problem even after production had
overcome expenditure by early 1943.
Torpedo Types
Three primary types of torpedoes were carried by U.S. submarines: the
Mark 10, the Mark 14, and the Mark 18. Both the Mark 10 and Mark 14
were steam powered, 21 inches in diameter and used T.N.T. at the war’s
beginning, but were converted to torpex by war’s end. The Mark 10 was the
standard torpedo on the earlier S-boats, while the Mark 14 was used on the
later fleet submarines, which were designed to accommodate its length.
At the war’s start, the Mark 10 had been in service on the older S-boats for a
decade. The warhead of the Mark 10 carried 497 pounds of T.N.T. in 1941; later
it was converted to carry 485 pounds of torpex. Fitted with the Mark 3 contact
detonator, the Mark 10 had a range of 3500 yards at a speed of 36 knots.
The Mark 14 was the latest in U.S. torpedo technology in 1941. While still
21 inches in diameter, it had been designed to be superior in almost every
way. The Mark 14’s normal range had been increased to 4500 yards at a
speed of 46 knots, but was also capable of a greater range of 9000 yards at a
lower speed setting of 31.5 knots (although in practice this was rarely
used). The warhead held 507 pounds of T.N.T. when first issued, but was
later improved to carry a 668-pound torpex payload. The crucial difference
between the Mark 14 and its predecessor was the Mark 6 detonator.
Between the World Wars, the Mark 6 detonator was developed to take advan-
tage of the magnetic field that ships created in the water around them.
Besides a contact detonator similar to that used in the Mark 3, the Mark 6
used a magnetic detonator. Designed to explode the warhead as the torpedo
passed through the target’s magnetic field, the magnetic detonator effectively
increased the target area. Conventional wisdom of the pre-war era held that
an explosion under the keel of the ship caused more damage because of the
presence of armor plating at the waterline and internal compartmentaliza-
tion. In theory, the Mark 14 would be a difficult weapon to evade.
History proved differently. For the sake of secrecy and economy, test firings
by submarines used a dummy warhead or were set to pass beneath the tar-
get vessel. This was to avoid damaging the ship or torpedo and accustom
SILENT
HUNTER
51 TORPEDOES: Shortages