If you've ever read a Tom Clancy novel, or watched one of the movies made from his books, you're likely to have heard a phrase such as, "Los Angeles-class submarine". The BBC's new series, Vigil, which just concluded, takes place on board a British nuclear submarine being shadowed by a Los Angeles-class American sub. What is a Los Angeles-class submarine, and what are the various 'classes' of US submarines? A 'class' is a single design that is used for a number of submarines, with later boats in the series often having improvements. Below, we're going to take a look at some of the US Navy's submarine classes throughout the years. Submarines are always referred to as boats and never as ships. Virginia-class submarineUSN/Wikimedia Commons 1775 to 1937 Turtle replica on display at the Royal Navy Submarine Museum Source: Geni/Wikimedia Commons The first US submarine, the USS Turtle, was built to attach explosive charges to the hulls of British ships during America's War of Independence. None of Turtle's attempts were successful. Alligator-class submarine Source: Wikimedia Commons Next came the Alligator-class, of which only one boat was made. She was built during the Civil War, and her main purpose was to protect the union's fleet of wooden ships against the Confederacy's ironclad frigate Merrimack, and she first set sail in 1861. In April, 1863, Alligator was being towed towards Charleston, South Carolina, when she was lost in bad weather off of Cape Hatteras, North Carolina. The USS Aligator was made of iron and was 14m long and had a beam of 1.42m. Air was supplied from the surface by two tubes connected to an air pump inside the submarine. Originally, Alligator was powered by 16 hand-powered paddles that protruded from her sides, but these were replaced by a hand-cranked propeller which got her up to four knots (7.4km per hour). By 1896, the US Navy commissioned the first Holland submarine, built by the Holland Torpedo Boat Company. This was the first commissioned submarine in the US Navy. Seven more of the boats were commissioned and built by Holland for the Plunger-class, which was later renamed the A-class, and they served primarily as training and experimental vessels. These boats had both an internal combustion engine for use on the surface, and an electric motor for use underwater. Plunger-class boats were the first with a reloadable torpedo tube and a deck gun, and they had ballast and trim tanks which allowed them to make precise changes in depth and attitude underwater. Next came a group of prosaically named classes, starting with the letter B in 1905 (the Plunger-class boats would be renamed as A-class in 1911), and ending with the letter S, built between 1917-1922. Each subsequent class featured improvements in design, for example, the D-class boats were able to survive flooding in one of their compartments. The E-class, in use between 1909 and 1912, were the first diesel-powered boats, while the L-class, built between 1914-1918, was the first built specifically for ocean-going. G-class submarine Source: Wikimedia Commons Operating between 1909 and 1914, G-class submarines were up to 49m, and they were able to reach 14 knots (7.2 metres per second) on the surface and 10.9 knots (5.6 metres per second) submerged. In 1911, six years before the Russian Revolution, the Russian Imperial Navy ordered 17 H-class boats Holland-type boats (which they confusing called American Holland-class). Eleven were delivered, but the shipment of the final six was held up by the outbreak of the Russian Revolution of 1917. These were eventually purchased by the US Navy, in 1918 and commissioned as H-4 to H-9 in late 1918. Built beginning in 1912, K-class boats were the first US submarines to see combat action when they participated in the First World War. The year 1916 saw the commissioning of three experimental AA-1-class boats, which were the first submarines designed to be fast enough to travel along with battleships. Though designed to travel at 14 knots (7.2 meters per second), the ships actually only achieved 11 knots due to a poor engine design and none of the boats saw active service. R-class submarine Source: Daniel Dunham/Wikimedia Commons Once the US entered the Great War in 1917, 20 R-class submarines were built. These had a larger conning tower, and they were the first to fire the Mark 10 torpedo. R-class boats could travel at 10.5 knots (5.4 metres per second) when submerged. The most successful of the Great War submarines were the S-class boats, of which 51 were manufactured between 1917 and 1922. The late 1920s and all of the 1930s saw a number of different classes of submarine being made, collectively called V-boats, and which featured names such as Barracuda, Argonaut, Narwhal, Dolphin, and Gato. 1937 to 1954 Between 1937 and 1939, the U.S. built 10 Sargo-class submarines. These boats were the first to be sent into action after the Japanese attack on Pearl Harbor. They were 95m and carried eight 53cm torpedo tubes, 24 torpedoes, and a 50-calibre deck gun. The 12 boats of the Tambor class, built in 1941, were 307 feet two inches long, and had four diesel engines and four electric motors. They had 10 x 53cm torpedo tubes with four aft, 24 torpedoes, and a 50-calibre deck gun. These boats were the US Navy's first practical fleet submarine and formed the core of the United States Pacific submarine fleet at the time of the US entry into the Second World War. Gato-class submarine Source: Wikimedia Commons From 1940 till 1944, the US manufactured 77 Gato-class submarines. They were 95m, and could reach speeds of 21 knots (11 metres per second) on the surface and nine knots (five metres per second) underwater. Most importantly, they had a range of 11,000 nautical miles and could reach a depth of 91m. This class was the standard attack submarine of the Second World War. Between 1942 and 1948, only two classes of submarine were manufactured: Balao-class, of which 122 were made, the first being the USS Devilfish. The Balao-class boats featured thicker steel in their pressure hull skins and frames which allowed them to dive to 122m. The Balao-class submarines were the workhorses during the Second World War. Balao-class submarine Source: Wikimedia Commons The other class of submarine used during the war was the Tench-class, of which 146 were scheduled to be manufactured. Only 29 were actually made. The rest were cancelled when it became clear the war was coming to an end and they would not be needed. 1954 to present During the Cold War years, the US continued making diesel-powered submarines, however, all that changed with the Nautilus-class of submarines, of which only one boat was made. The USS Nautilus was launched in 1954, and she was the world's first nuclear-powered submarine. Before Nautilus, diesel-powered submarines had to surface often because their engines need a steady supply of oxygen to burn fuel. So, they would surface in order to run the engines and charge their batteries. Under nuclear power, however, a boat could stay underwater for months at a time, constrained only by the amount of food it could carry. USS Nautilus Source: USN/Wikimedia Commons The Nautilus was 91m, able to carry more than 100 crew members, and she was propelled by a 13,400 horsepower (10.0MW) nuclear reactor capable of achieving 23 knots (12 metres per second). Between 1956 and 1961, six boats of the Skipjack-class were made. The Skipjack boats also featured a teardrop hull (developed for the Barbel-class, which was built between 1956-1959), and they carried a new nuclear reactor, the S5W. This reactor was also used in the first British nuclear submarine, the HMS Dreadnought. One of the Skipjack-class was the USS Scorpion which was lost at sea, with all hands, in 1968. Thresher-class submarine Source: Wikimedia Commons Between 1958 and 1968, the 14 Thresher-class boats were the first submarines to have a bow-mounted sonar sphere. They also featured improved pressure hulls that allowed them to dive to 396m. The entire class was renamed the Permit class after the USS Thresher was lost in 1963. Los Angeles-class submarine Source: Wikimedia Commons In 1972, came the Los Angeles-class of fast attack submarines, and 62 were built. The Los Angeles-class is the most numerous nuclear-powered submarine class in the world, and with one exception, all the boats in the class are named after US cities. The exception is the USS Hyman G. Rickover, which is named for the man considered to be the 'father of the nuclear Navy'. The first member of the class was the USS Los Angeles, which was commissioned in 1972, and the last member of the class was the USS Cheyenne, which was commissioned in September 1996. The final 23 boats in the class were designed for under-ice operations, with their diving planes being located on the bow rather than on the sail. These final 23 boats are also quieter than their predecessors and incorporate a more advanced combat system. Sub under the ice Source: U.S. Naval Academy Submarines today Today, the US operates three types of submarines: Attack Submarines (SSN), Ballistic Missile Submarines (SSBN), and Guided Missile Submarines (SSGN). The three classes of attack submarines are the Los Angeles, Seawolf, and Virginia-class. Their purpose is seek-and-destroy missions, surveillance and reconnaissance, covert troop insertion, and mine and anti-mine operations. They also carry cruise missiles. As of this writing, there are 34 Los Angeles-class submarines on active duty. The US also deploys three Seawolf-class submarines, which are exceptionally quiet and fast, nineteen Virginia-class boats (with more under construction). One of the Seawolf boats, the USS Jimmy Carter, is sometimes placed in a sub-class of its own, as it has been specially modified with a 100ft hull extension, called the multi-mission platform, which can accommodate the advanced technology used to carry out classified research and development. According to an August 4, 2021 article in Forbes magazine, in an unusual move, the U.S. deployed all three of its Seawolf-class boats – the USS Seawolf, USS Connecticut, and USS Jimmy Carter in the Pacific Ocean this past July. Ballistic Missile Submarines, also known as 'Boomers', serve as part of America's strategic nuclear deterrent, and they are capable of operating underwater for months at a time. The distinguishing feature of Guided Missile Submarines is their stealth, and members of this group include Ohio-class boats. In the years to come, Virginia-class boats will replace the Los Angeles-class boats as they retire. The picture at the top of this article is of a Virginia-class submarine. These boats feature a fly-by-wire ship control system that improves shallow-water handling, and they have a reconfigurable torpedo room that can be used to support divers. In Virginia-class boats, the traditional periscopes have been replaced by two photonics masts that have both visible and infrared digital cameras atop telescoping arms. Without the need for the barrel periscopes used in previous submarines, the control rooms of Virginia-class boats have been moved down one deck, allowing for more room. The Virginia-class makes use of modular construction, open architecture, and commercial off-the-shelf components, which will allow it to remain state-of-the-art for its entire operational life. If you want to catch a glimpse of one of these titans of the deep, their home ports are: Groton, Connecticut, Norfolk, Virginia, Pearl Harbor, Hawaii, San Diego, California, and Apra Harbor, Guam.