The Mark 14 Torpedo, A Tale of Triumph

How the US Navy transformed the problematic Mark 14 Torpedo into a game changer during World War II.

The Mark 14 torpedo was the backbone of the United States Navy’s submarine-launched arsenal during World War II. Yet its journey from development to deployment was anything but smooth. 

Plagued by problems—from running too deep to premature explosions—this torpedo became the center of a scandal within the US Submarine Force. However, after nearly two years of relentless troubleshooting, the Mark 14 eventually emerged as a reliable weapon that would help deliver crushing blows to the Japanese Imperial Navy. 
This is the story of the Mark 14 torpedo, its troubled origins, the controversies that surrounded it, and its eventual transformation into a symbol of innovation.

A Bold New Concept

Design of the Mark 14 torpedo began in January 1931 with a modest allocation of $143,000. Intended to replace the aging Mark 10 torpedo, the new weapon was built for the fleet submarines of a modern Navy. Although it shared the same diameter as its predecessor, the Mark 14’s length of 20 feet 6 inches rendered it incompatible with older submarine tubes. Over time, production adjustments even led to shortened versions to meet operational needs.

Technical Innovations

The Mark 14 introduced several innovations designed to enhance torpedo performance:

• Propulsion and Speed: Improved power allowed the torpedo to reach speeds up to 46 knots (85 km/h), a significant jump from the 30-knot performance of the earlier Mark 10.
• Guidance and Depth Control: Steering was managed by a continuously powered gyro and enhanced depth stabilization—though these systems would later become sources of trouble.
• The Mark 6 Exploder: Central to its design was the sophisticated Mark 6 magnetic influence exploder. Developed in secrecy starting in 1922, it was intended to detonate the torpedo beneath a target’s keel, bypassing a ship’s armor.

Despite these cutting-edge features, the Mark 14’s early days were marred by inadequate testing and a reluctance to conduct live-fire trials, primarily due to the high cost of these weapons during the Depression era.

The Torpedo Scandal

The Mark 14 became notorious as the centerpiece of a torpedo scandal within the Pacific Submarine Force. Inadequate production led to severe shortages, while frugal peacetime testing left many serious design flaws undiscovered. With torpedoes costing around $10,000 (equivalent to about $200,000 today), the Navy was reluctant to sacrifice them in live-fire tests. This cautious approach, however, meant that critical defects were not identified until they were in combat.

Faulty Assumptions and Overlapping Defects

Much of the blame for early failures fell on the Mark 6 exploder, which suffered from a rigid sensitivity setting and was never adequately live-tested. When torpedoes would run under targets or explode prematurely, it became difficult to pinpoint the exact cause because multiple flaws tended to mask one another. 

Additionally, the Bureau of Ordnance’s (BuOrd) limited budget and unrealistic testing protocols contributed to the problem. Responsibility for these oversights was also shared by Congress, which had slashed funding during the interwar years, and by the Naval Torpedo Station (NTS), whose testing efforts proved woefully inadequate.

Major Flaws and Problems

The Mark 14 torpedo suffered from four primary defects that plagued its early use in combat:

Running Too Deep

One of the most persistent issues was that the torpedo tended to run about 10 feet (3 m) deeper than set. Several factors contributed to this:

• Test Conditions vs. Reality: The torpedo was originally tested using a buoyant exercise warhead. In contrast, the live warhead, being heavier, caused the torpedo to settle deeper.
• Pressure Port Placement: A critical design flaw in the depth control mechanism arose when the pressure sensor was moved to the cone-shaped tail. In certain conditions, hydrodynamic effects reduced the pressure reading, causing the torpedo to trim deeper.
• Impact of Speed: Higher speeds exacerbated the depth issue, a problem that only began to be addressed in the latter half of 1943 by relocating the sensor to the midbody.

Magnetic Influence Exploder and Premature Explosions

The innovative Mark 6 magnetic exploder was designed to detonate the torpedo beneath a target. However, its performance was far from reliable:

• Premature Detonations: The exploder would often trigger too early, either when the torpedo was still adjusting its course or just before reaching the target, leading to premature explosions that caused little or no damage.
• Misinterpretation of Failures: As torpedoes began running at the correct depth, submarine commanders initially believed that failures were solely due to the magnetic exploder, leading some to disable its function entirely—often against orders.

Contact Exploder Failures

Compounding the problems was the contact exploder, intended to detonate upon impact:

• Binding Issues: The Mark 14’s contact exploder, descended from the older Mark 3 design, was not suited for the high speeds of the Mark 14. The impact deceleration caused the firing pin to bind, resulting in duds even when a torpedo struck directly.
• Angle of Impact: Ironically, a perfect 90-degree hit often failed to trigger the explosion, whereas oblique angles, which were less than ideal, were more likely to work.

Circular Runs

Another perilous flaw was the tendency for the torpedo to run in a circular pattern:

• Gyro Malfunctions: In some instances, failure to properly install the gyro, or its design limitations, led to a torpedo circling back toward its firing vessel. There were reports of torpedoes that nearly sunk their own submarines due to these circular runs.

The Struggle for Resolution

Despite mounting evidence of failure, it took almost two years to isolate and rectify the Mark 14’s problems. Relentless field testing by submarine commanders, such as Commander Tyrell Jacobs and Rear Admiral Charles Lockwood, finally highlighted the weapon’s deficiencies.

Deactivation of the Magnetic Exploder

By mid-1943, after multiple premature detonations and mounting casualties from dud hits, pressure mounted for action. Although initial resistance came from high-ranking officers reluctant to waste scarce torpedoes, persistent demands from front-line commanders eventually led to a decision. 

On 24 June 1943, under orders from the Commander-in-Chief of the Pacific Fleet, all submarines were instructed to deactivate the magnetic influence feature. This measure, while not an ideal solution, paved the way for subsequent improvements.

Fixing the Contact Exploder and Depth Control

Following the deactivation of the magnetic exploder, problems with the contact mechanism became more evident. Through testing, the Navy identified the binding issue and implemented design modifications. By replacing heavier materials with lighter aluminum parts and adopting a stiffer spring in the contact mechanism, the Navy finally achieved a reliable detonation system. Meanwhile, relocating the depth sensor in the torpedo’s design corrected the deep-running issue.

Resolution and Legacy

With the fixes implemented by the end of 1943, the Mark 14 torpedo’s performance improved dramatically. Sinkings of enemy ships rose, and the torpedo became a key factor in the success of US submarines during the Pacific campaign. Despite its early shortcomings, the Mark 14 went on to remain in service for nearly 40 years.

The hard-won lessons from the Mark 14’s troubled development influenced subsequent torpedo designs. Its best features were later integrated with innovations gleaned from captured German torpedoes, leading to the development of the hydrogen peroxide–fueled Mark 16 torpedo. 

Reliable Thoughts – A Lesson on Improvement

The story of the Mark 14 torpedo is one of trial, error, and eventual triumph. Its early life was defined by a cascade of design flaws, inadequate testing, and the harsh realities of war. Yet, through persistent testing, courageous leadership, and relentless ingenuity, the Navy transformed a problematic weapon into a dependable tool.