snorkel (naval)

snorkel (naval). A naval snorkel is a retractable mast system that allows a submarine to operate its diesel engines while submerged at periscope depth, drawing air from above the surface and expelling exhaust gases. This innovation, also known as a schnorchel from its German development, significantly extended a submarine's underwater endurance and reduced its vulnerability to detection by Allied aircraft and warships during World War II. While initially pioneered by the Dutch Navy before the war, the technology was most extensively developed and deployed by Germany's Kriegsmarine in the latter stages of the Battle of the Atlantic.

History and development

The concept for a submarine air mast was first explored by the Royal Italian Navy as early as the 1920s, but the first practical system was invented by the Dutch Navy in the 1930s, intended for their O 21-class submarines. Following the German occupation of the Netherlands in 1940, German engineers discovered the Dutch designs and accelerated their own development program at Kiel and Wilhelmshaven. The Kriegsmarine initially resisted the device, but heavy losses inflicted by RAF Coastal Command and United States Navy hunter-killer groups during the Black May crisis of 1943 forced its rapid adoption. By 1944, under the direction of Grand Admiral Karl Dönitz, snorkels were being retrofitted to Type VII and Type XXI U-boats. Post-war, the technology was evaluated and adopted by the Royal Navy, United States Navy, and Soviet Navy, becoming a standard feature on diesel-electric submarines during the Cold War.

Design and operation

A basic snorkel system consists of two primary masts: an air intake mast and a separate exhaust mast. The intake mast features a head-valve designed to automatically seal if submerged by a wave, preventing water from flooding the diesel engine. The exhaust mast expels gases from the engine below the waterline, though this created a visible bubble plume and increased backpressure on the engine. Key components included a radar warning receiver, often the FuMB Antenna 3 Bali, mounted atop the mast to detect enemy ASDIC and X-band radar emissions from ships like the HMS *Starling*. Operation required the submarine to maintain a precise depth and speed, typically around six knots, with the entire system controlled from the control room via hydraulic rams.

Military applications and use

The snorkel's primary military application was to allow U-boats to recharge their batteries and cruise while remaining submerged, drastically reducing their visible silhouette and vulnerability to Allied aircraft such as the B-24 Liberator. This transformed submarine tactics in the Battle of the Atlantic, forcing Western Approaches Command to develop new countermeasures. During the Cold War, snorkeling became a routine procedure for diesel-electric submarines of the Soviet Navy's Whiskey-class and the Royal Swedish Navy, enabling covert intelligence gathering and extended patrols in contested areas like the GIUK gap. Modern air-independent propulsion systems have reduced, but not eliminated, the need for snorkeling.

Advantages and limitations

The chief advantage was a massive increase in submerged endurance, allowing a U-boat to remain underwater for weeks instead of days, which complicated the efforts of Royal Canadian Navy and United States Navy escort groups. However, significant limitations included reduced speed while snorkeling, excessive noise from the diesel engines and exhaust, and the creation of a distinct radar signature detectable by units like the USS *Bogue*. The system was also unreliable in rough seas, as wave action could cause the head-valve to "slam," temporarily depriving the engines of air and creating a hazardous vacuum within the submarine's pressure hull.

Notable installations and variants

The most famous installations were on the late-war Type XXI Elektroboote, which integrated the snorkel into its streamlined design. The United States Navy extensively tested captured Type XXI boats, including U-3008, influencing the design of the Tang-class submarine. The Royal Navy developed its own "snort" mast for the T-class submarine and Porpoise-class submarine. Unique variants included the complex system on the French Navy's *Gymnote* (S655), a testbed for M45 missile systems, and the integrated masts on the Japanese Maritime Self-Defense Force's Sōryū-class submarine.

Category:Submarine technology Category:Military equipment of World War II Category:Naval engineering