129 American sailors die when the submarine USS Thresher sinks at sea.

A submarine, often simply called a "sub," represents a marvel of engineering: a sophisticated watercraft uniquely designed for independent operation beneath the waves. This remarkable capability sets it apart from a submersible, which typically possesses more limited endurance and operational autonomy underwater, often requiring support from a surface vessel or shore. Historically and even colloquially today, the term "submarine" might sometimes broadly encompass remotely operated vehicles (ROVs), autonomous underwater vehicles (AUVs), and various smaller craft like midget submarines or "wet subs" – though these often serve highly specialized niches.

Interestingly, despite their often immense size, submarines are almost universally referred to as "boats" rather than "ships" within naval tradition. This nomenclature harks back to their early days when they were indeed much smaller and often carried aboard larger vessels. It’s a cultural detail that persists, reflecting a unique identity within the maritime world.

The Evolution of Underwater Exploration and Warfare

While experimental designs for underwater craft emerged much earlier, true submarine development began to accelerate significantly during the 19th century. Innovators worldwide contributed to designs that eventually allowed for practical underwater navigation. By the turn of the 20th century, several navies had recognized their potential and started incorporating them into their fleets. However, it was during the tumultuous years of World War I (1914–1918) that submarines first saw widespread and impactful use, reshaping naval strategy forever. Today, they are indispensable assets for navies globally, from the largest powers to smaller maritime forces.

Diverse Roles: From Military Might to Scientific Endeavor

The applications for submarines are incredibly varied, spanning critical military functions and vital civilian pursuits.

Architectural Ingenuity: The Design of a Submarine

Modern deep-diving submarines owe much of their lineage to earlier experimental craft, particularly the bathyscaphe, which itself evolved from the even older concept of the diving bell. These historical predecessors laid the groundwork for understanding the immense pressures of the deep sea.

Most large submarines share a distinctive foundational design: a robust cylindrical body, capped at both ends with strong hemispherical or conical structures to withstand pressure. Prominently situated amidships on the top is a vertical structure known as the "sail" in American naval terminology, or the "fin" in European usage. This structure isn't just for aesthetics; it houses crucial communications and sensing devices, along with periscopes, enabling observation and navigation when near the surface. Earlier designs featured a separate "conning tower"—a smaller pressure hull positioned above the main body—which allowed for the use of shorter periscopes and provided a more sheltered observation post. At the rear, a powerful propeller or a more modern pump-jet propulsion system drives the vessel, complemented by various hydrodynamic control fins that enable precise maneuvering underwater.

It's important to note that not all submarines adhere strictly to this traditional design. Smaller, highly specialized, or extreme deep-diving submarines often deviate significantly, adopting unique shapes tailored to their specific missions, whether for greater maneuverability, deeper dives, or specific scientific tasks.

Mastering the Depths: How Submarines Dive and Resurface

The fundamental principle behind a submarine's ability to dive and resurface lies in controlling its buoyancy, a concept rooted in Archimedes' principle. This is achieved primarily through diving planes (hydrodynamic control surfaces similar to an airplane's wings, which can be angled to create lift or depression) and, more crucially, by precisely managing the amount of water and air within its ballast tanks. To dive, large vents on the top of the ballast tanks are opened, allowing seawater to flood in and displace the air. As the submarine becomes denser (heavier) than the surrounding water, it begins to sink. To resurface, high-pressure air is blown into the ballast tanks, expelling the seawater. This reduces the submarine's overall density, making it lighter than the water, and causing it to rise to the surface. This delicate balance of weight and displacement allows for controlled ascent and descent.

A Spectrum of Size and Capability

Submarines boast one of the widest ranges of types and operational capabilities of any vessel known to humankind. Their diversity is truly remarkable. At one end of the spectrum, there are tiny autonomous examples and compact one- or two-person subs designed for missions lasting just a few hours. At the other extreme are colossal vessels like the Russian Typhoon class, which are not only the biggest submarines ever constructed but are also capable of remaining submerged and operational for an astonishing six months or even longer, carrying immense stores and provisions for their large crews. This extraordinary capability allows submarines to operate effectively at depths far beyond what is survivable or practical for human divers, extending humanity's reach into the ocean's most challenging environments.

A Tragic Milestone: The Loss of USS Thresher (SSN-593)

The USS Thresher (SSN-593) holds a poignant place in naval history as the lead boat of her class of nuclear-powered attack submarines within the United States Navy. Fittingly, she was the second U.S. Navy submarine to bear the name of the distinctive thresher shark, known for its powerful tail.

Tragically, on April 10, 1963, the Thresher was lost during deep-diving tests approximately 350 kilometers (about 220 miles) east of Cape Cod, Massachusetts. The incident resulted in the catastrophic loss of all 129 crew members and shipyard personnel aboard. This profound tragedy stands as the second-deadliest submarine incident on record, surpassed only by the 1942 sinking of the French submarine Surcouf, which claimed 130 lives.

The loss of the Thresher served as an agonizing watershed moment for the U.S. Navy. It catalyzed the immediate and comprehensive implementation of a groundbreaking, rigorous submarine safety program known as SUBSAFE. This program, which revolutionized design, construction, maintenance, and operational procedures, has since been credited with significantly enhancing the safety and reliability of the U.S. submarine fleet. Beyond being the first nuclear submarine lost at sea, the Thresher was also the third of four submarines that have tragically been lost with more than 100 people aboard in recorded history. These include the USS Argonaut, lost with 102 aboard in 1943; the aforementioned Surcouf, which sank with 130 personnel in 1942; and the Russian submarine Kursk, which was lost with all 118 aboard in 2000.

Frequently Asked Questions (FAQs)

What is the primary difference between a submarine and a submersible?
The main distinction lies in their operational independence and duration. A submarine is designed for independent, sustained underwater operation over long periods, often weeks or months. A submersible, conversely, has more limited underwater capabilities, typically operating for shorter durations and often requiring support from a surface vessel for deployment, recovery, and power.
Why are submarines called "boats" and not "ships"?
This is a naval tradition originating from the early days of submarines when they were much smaller and considered specialized craft, often carried aboard larger "mother ships." The term "boat" persisted as a cultural identifier even as submarines grew immensely in size and capability, distinguishing them from surface warships.
What are the main military roles of a modern submarine?
Modern military submarines serve numerous critical roles, including attacking enemy surface vessels and other submarines, protecting aircraft carrier groups, conducting strategic nuclear deterrence (carrying ballistic missiles), performing covert reconnaissance, launching conventional land attacks with cruise missiles, and inserting or extracting special forces behind enemy lines.
How do submarines dive and resurface?
Submarines control their buoyancy using ballast tanks and diving planes. To dive, they flood their ballast tanks with seawater, making the submarine heavier than the surrounding water. To resurface, high-pressure air is used to expel the seawater from the ballast tanks, making the submarine lighter and causing it to ascend.
What was the significance of the USS Thresher's sinking?
The tragic loss of the USS Thresher in 1963, with all 129 personnel, was a pivotal event for the U.S. Navy. It led directly to the establishment of the rigorous SUBSAFE program, which revolutionized submarine design, construction, maintenance, and operational safety, significantly improving the safety record of the entire U.S. submarine fleet.
What is the largest submarine ever built?
The largest submarines ever built are the Russian Typhoon class ballistic missile submarines, renowned for their immense size and long-endurance capabilities.