The Momsen Lung was a submarine escape device invented in the early 1930s by Charles Momsen, following several submarine disasters that underscored the urgent need for reliable escape technology.

It operated as a rebreather, removing carbon dioxide and replenishing oxygen in exhaled air, enabling submariners to breathe underwater while ascending to the surface.

This device significantly enhanced submarine crew safety, providing a personal escape mechanism that improved the odds of survival in emergencies.



The impetus for developing submarine escape technology stemmed from the inherent risks associated with early submarine operations. Submarines, often referred to as “iron coffins,” were fraught with dangers due to their rudimentary design and the lack of reliable safety measures. The closed, pressurized environment of a submarine, coupled with the volatile nature of its early power systems, often led to accidents that could easily become fatal for the crew trapped within.

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The need for a reliable escape mechanism became increasingly apparent following several catastrophic submarine disasters. For instance, the sinking of the USS S-4 in 1927 profoundly impacted the U.S. Navy, as the submarine was struck by a Coast Guard cutter off Provincetown, Massachusetts. Despite the submarine being relatively close to the surface and rescue efforts being promptly initiated, all 40 crew members perished, primarily because there was no effective method for them to escape the disabled sub.

USS S-4 after being salvaged in 1928.

Such incidents underscored a critical vulnerability in submarine safety and galvanized the naval leadership to seek solutions. The absence of escape options not only jeopardized the lives of the submariners but also deterred potential recruits, affecting the operational readiness and strategic capabilities of the navy. The pressing need to enhance submariner survivability and maintain the viability of underwater vessels as strategic assets was clear, leading to increased investments in research and development of escape technologies.

Charles Momsen

Charles Momsen, a naval officer with a background in engineering, was deeply affected by the recurrent tragedies involving submarine crews. His motivation to find a solution was intensified by the inadequacy of existing rescue methods, which were often slow, unreliable, and ineffective in actual crisis situations.

The loss of life in submarine disasters such as the USS S-4 tragedy, where rescuers could hear the trapped sailors’ hammering for help as they ultimately succumbed, had a profound impact on him. These experiences drove Momsen to advocate for and develop better submarine rescue technologies.

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In the late 1920s, Momsen began experimenting with various concepts and designs aimed at enabling submariners to escape from sunken submarines. His pioneering work led to the creation of the Momsen Lung, a device designed to be simple yet effective, ensuring that it could be operated even under stressful conditions.

The device was a type of rebreather, which recycled exhaled air by scrubbing out carbon dioxide and replenishing oxygen, thereby allowing the user to breathe underwater independently from the submarine’s atmosphere.

A Momsen Lung on display in the Marinmuseum, Karlskrona, Sweden.

Momsen’s approach was revolutionary because it offered a portable solution that gave individual submariners the agency to escape, rather than relying solely on external rescue operations, which could fail or not reach the stranded crew in time.

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The invention was not just a technical achievement but also a logistical success, as Momsen worked diligently with the U.S. Navy to ensure the widespread adoption and deployment of the Momsen Lung. He conducted numerous training sessions and drills, dramatically demonstrating the device’s effectiveness and building confidence among the submariners. Momsen’s commitment to improving naval safety was instrumental in transforming submarine rescue operations.

Design of the Momsen Lung

The design and functionality of the Momsen Lung were carefully engineered to address the specific challenges of escaping from a disabled submarine. The device itself is a compact, self-contained rebreather system designed to be worn like a backpack, allowing for hands-free operation which is crucial during an underwater escape.

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Core Components and Mechanism: The Momsen Lung consists of several key components that work together to facilitate breathing under water:

  1. Breathing Bag: This rubberized fabric bag serves as the lung’s primary air reservoir. It holds a mixture of recycled exhaled air and pure oxygen, which is critical for the rebreathing process.
  2. Oxygen Supply: A small, pressurized oxygen tank is connected to the breathing bag. This supplies the necessary oxygen to replenish what the submariner consumes and ensures the air mixture remains breathable.
  3. Carbon Dioxide Scrubber: The device includes a canister filled with soda lime, a chemical compound that absorbs carbon dioxide from the user’s exhaled air. This scrubbing action prevents carbon dioxide buildup, which could lead to hypercapnia and respiratory distress.
  4. Mouthpiece and Nose Clip: These components ensure that the submariner breathes only through the mouthpiece, which is directly connected to the breathing bag. The nose clip prevents breathing in potentially contaminated air from the surrounding environment inside the submarine.

Operational Procedure: To use the Momsen Lung, the submariner would first secure the device around their chest, engage the nose clip, and place the mouthpiece securely in their mouth. Upon breathing, the exhaled air would pass through the scrubber canister, where carbon dioxide is removed. The cleaned air, along with a fresh supply of oxygen from the tank, is then inhaled back through the mouthpiece.

Buoyancy and Ascension Control: An essential feature of the Momsen Lung’s design is its ability to aid in controlled ascent to the surface. The rebreather’s bag expands as it is filled with the exhaled air, which is slightly buoyant. This buoyancy aids the submariner in ascending without the need for excessive swimming effort, which could lead to exhaustion. The submariner could control their ascent rate by releasing air from the bag if needed to slow the rise or prevent too rapid an ascent, which could cause decompression sickness.

A crewman of the USS V-5 exiting the submarine wearing a Momsen Lung, July 1930.

Innovative Design Elements: The innovative design of the Momsen Lung addressed the practical needs of submariners in emergency situations. Its relatively simple and robust construction meant it could be reliably used in the high-stress, often chaotic conditions following a submarine accident. The device’s independence from the submarine’s power or air systems was a crucial feature, ensuring it would function even in the direst scenarios.

Operational Use of the Momsen Lung

Upon its introduction in the 1930s, the Momsen Lung quickly became a critical part of the safety equipment aboard U.S. submarines. Its adoption marked a significant shift in the way submarine crews approached underwater emergencies, providing them with a viable means of escape that had not previously existed. The device was distributed widely among the submarine fleets, and extensive training regimes were established to ensure that every submariner was proficient in using it.

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The operational use of the Momsen Lung involved regular drills where crew members practiced escaping from submerged mock-ups or actual submarines in controlled conditions. These exercises were crucial not only for building skills but also for instilling confidence among the crews, demonstrating that survival from a disabled submarine was possible. Despite the potential for panic or disorientation during an actual escape, the training helped submariners master the calm, methodical breathing necessary to make effective use of the device.

A pair of Momsen Lungs currently on display on board the museum ship USS Drum. Image by LittleT889

The impact of the Momsen Lung was profound both psychologically and practically. Psychologically, the presence of the Momsen Lung on board provided submariners with a greater sense of security and morale, knowing they had a personal escape device in case of an emergency. Practically, it enhanced survival rates during submarine accidents by offering an escape option where none had existed before, thereby potentially saving lives that would have otherwise been lost in sunken submarines.

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Furthermore, the Momsen Lung’s influence extended beyond its immediate life-saving function. It spurred additional innovations and improvements in submarine safety and escape technology. The introduction of the Momsen Lung led to the development of other escape devices like the Steinke hood and eventually more advanced submarine escape immersion suits and escape capsules, which provided even greater protection and functionality for submariners.