A Spotter's Guide to Modern Warships

Over the 70 years since the end of WW2, the nomenclature of warships has become very confused. This is for several reasons. The demise of the treaty structure removed the legal restrictions preventing categories merging. The minimum size of ship required for effective operations grew, while at the same time the need for numbers held down sizes on the top end. Different countries adopted different naming schemes for political or historical reasons, and classifications evolved over time. I’ll do my best to explain all of this, but it is of necessity an imperfect science. This list skews a bit towards what you'd see on the oceans today, or at least since the 80s, but it should be helpful in understanding what was going on since the 60s, or even earlier in combination with the previous list.

First, some definition of the weapons is necessary:

• Guns: Typical modern naval guns run from 3 to 5". They are of limited use against low-performance aircraft and incoming missiles, but are often valuable for shore bombardment and firing shots across the bows of merchant ships to get their attention.
• PD SAM (Point-Defense Surface-to-Air Missile): A PD SAM is designed to protect the ship it's mounted on, and maybe the ship next to it, against incoming anti-ship missiles or airplanes flying really low. It is not effective at protecting a group, or at shooting down aircraft at altitude.
• MR SAM (Medium-range SAM): An MR SAM is an area-defense weapon. It's a threat to airplanes at significant altitude and range, and also has some capability against missiles.
• LR SAM (Long-range SAM): A higher-powered variant of an MR SAM. More range, and probably a ballistic-missile defense capability in modern ships.
• SSM (Surface-to-Surface Missile): A SSM is a weapon designed to kill other ships. There are two basic varieties. First, small, subsonic weapons designed to kill frigates, such as Harpoon. These are very common, but are unlikely to sink even a frigate outright. They'll badly wound a larger ship, but not kill it. Second, large, supersonic missiles designed to kill big ships. These are mostly Russian in origin, intended to be fired at US carriers.
• ASW (Anti-Submarine Warfare) launcher: A weapon that fires depth charges ahead of or to the side of the ship. These are unguided and have relatively short range.
• ASW torpedo: A small homing torpedo. Short-ranged, and usually has to be dropped pretty much right on top of the submarine to be effective.
• ASW missile: A long-range ASW weapon, usually a missile fitted with a homing torpedo for a head.
• CIWS (Close-In Weapons System): An automatic gun, usually 20-30 mm, with an attached radar. Intended to shoot down incoming SSMs autonomously.
• Torpedo tube: A large tube for launching underwater weapons. Found mostly on submarines these days. Most common weapon is the heavy torpedo, useful against both surface ships and submarines. Some can fire SSMs, ASW missiles and cruise missiles, too.
• Cruise missile: A land-attack missile such as Tomahawk, fired from a warship. Several hundred mile range, warhead ~1000 lbs. Can often be launched from modern ships equipped with MR or LR SAMs.
• Helicopter: Probably the main weapon of many modern surface combatants. Capable of many roles: moving people and things around, hunting submarines, and patrolling for and attacking surface vessels.

Now, onto the ships:

• Frigate:¹ The most common type of modern surface warship. A vessel of 2,000-4,000 tons, equipped with 1-2 guns, some combination of ASW launchers, torpedoes, and ASW missiles, and a helicopter. May also carry SSMs, PD SAM systems and/or CIWS. Split between general-purpose surface warships, and specialized ASW escorts. 27-32 kts. Also called a destroyer or destroyer escort.
• Destroyer: A slightly larger surface warship than a frigate. 3,000-8,000 tons, with 1-2 guns, CIWS and some combination of ASW weapons. Usually has an MR SAM, 4-8 SSMs and 1-2 helicopters. 30-36 kts. Normally intended as an anti-air escort, sometimes as a heavy ASW ship or an anti-surface platform. Current usage appears to be standardizing on ships with area-defense SAMs.
• Cruiser: A heavier, larger version of the destroyer. 7,000-20,000 tons. 1-2 guns, CIWS, some ASW weapon(s) and LR SAM. SSMs and helicopters are common. Usually a heavy AAW escort, sometimes an anti-ship platform. 30-33 kts. Currently overlaps with the largest destroyers, which appear to be replacing them, as none have been built since the end of the Cold War.
• Corvette: A smaller version of a frigate, usually without a helicopter. 500-2,000 tons. ASW weapons, 1-2 guns, and SSMs are common, some have PD SAM. Some specialize in ASW, although most are general-purpose. 30 kts.
• Helicopter Cruiser: A ship that's the back half of a carrier welded to the front of a cruiser. 6,000-15,000 tons. Weapons can include MR SAM, Gun, CIWS and ASW weapons. 3-15 helicopters. 30 kts. Used to deploy large numbers of helicopters for ASW.
• Helicopter/VTOL Carrier: A ship designed for carrying ASW helicopters and VTOL aircraft. 10,000-36,000 tons. Some are armed only for self-defense (PD SAM and CIWS) while others have MR or LR SAMs, ASW weapons and SSMs. 20-30 aircraft. 28-30 kts. Used for sea control and very light strike missions. Sometimes given misleading names like "helicopter destroyer", "aviation cruiser" or "through-deck command cruiser" for legal/political reasons.
• Aircraft Carrier, Small: A ship that carries conventional airplanes to sea. Some left over from WW2, others new-built. 30,000-70,000 tons, 40-60 aircraft. Guns, CIWS, and PD SAM are common. 30-32 kts. Used for sea control, ASW, and strike missions.
• Aircraft Carrier, Large: A very large ship that carries conventional aircraft to sea. Often nuclear powered. 70,000-100,000 tons, 90 aircraft. CIWS and PD SAM. 30 kts. Similar missions to small aircraft carriers, but more capable.
• Submarine, early diesel: A submarine, designed for greater underwater performance than the submarine of WWII, inspired by German Type XXI. Some converted, others new-built. 1,000-2,500 tons, 6-8 torpedo tubes, sometimes deck guns. 13-18 kts submerged. Used for anti-ship missions.
• Submarine, diesel: A submarine designed entirely for underwater operations. Limited mobility, but very stealthy. 1,200-3,000 tons, 6-10 torpedo tubes. 15-25 kts submerged. Used for anti-ship and anti-submarine missions.
• Submarine, nuclear attack: A submarine capable of true underwater operation. Capable of sustaining high underwater speeds indefinitely, never has to snorkle. 3,500-9,000 tons. 4-8 torpedo tubes, some carry missiles. 25-45 kts submerged. Used for anti-ship and anti-submarine missions, some have land strike capability.
• Submarine, guided missile: A submarine intended to attack ships with cruise missiles. Most nuclear-powered. 6,000-18,000 tons. 4-8 torpedo tubes, 8-24 cruise missiles. 23-33 kts submerged. Used for attacking heavy surface ships. Rare today.
• Submarine, ballistic missile: A submarine armed with nuclear ballistic missiles. Very quiet, nuclear-powered. 8,000-25,000 tons. 4-6 torpedo tubes, 16-24 nuclear missiles. 20-25 kts submerged. Intended for destroying the world if necessary. So far, it hasn't been.
• Minesweeper/Minehunter: A small, low-signature ship designed to deal with mines. 150-1,000 tons. 1 small gun, mine countermeasures equipment. 10-15 kts.
• Torpedo Boat: A small, fast ship intended to fire torpedoes. 2 small guns, 4 torpedoes. 60-200 tons. 40-50 kts. For protecting coastal waters.
• Missile Boat: A small ship intended for missile attack. 2-4 small guns, 4-8 missiles. 200-400 tons. 30-45 kts. Coastal defense.
• Offshore Patrol Vessel (OPV): A ship intended for presence roles in coastal waters, by the Coast Guard or equivalent. 1-2 guns, may be fitted for but not with heavier weapons. 20-30 kts. Cheap, with a focus on seakeeping and high availability, and without the combat systems of proper warships. Larger ones have a helicopter.

As with the last list, I'm excluding amphibious ships and auxiliaries, which are covered elsewhere.