Ship classifications used in this guide are drawn from real-world naval terminologies and then adapted to strategies and realities which exist in-game in Space Engineers. What this means is that while every classification described is based on a real-world ship classification, each one may differ in significant ways from their real-world counterparts.

Additionally, the guidelines presented here serve two purposes:
1.) To provide players with flexible descriptions that allow them to name their ships as they like. This means mass ranges and weapon layout descriptions will have overlap between classes described. This is intentional, and ships may end up qualifying for multiple classes or appearing to be hybrids between two or more classes. This is okay, and intended.

2.) To provide guidelines for players to design ships which are competitive and can be balanced against each other for prepared battles. For example, if you are preparing a large PvP battle and you want both sides to have X Frigates, Y Cruisers, and Z Battleships now you will be able to point to some guidelines to help balance those designs against each other.

DISCLAIMER: Classifications list weapon types in ranges from minimum to maximum. This does not however mean that a ship that has the maximum number of Turrets should also have the maximum number of Rocket Launchers. These are descriptive guidelines only. Ship classes with very high Rocket Launcher counts are often ship classes which assume broadsides, like the Cruisers. This does not mean a Heavy Cruiser should have 30 Rocket Launchers facing in one direction, but up to 15 on each side (not counting constructed turrets).

source - Hull classification symbols[en.wikipedia.org]

The alphanumeric code generated from this system will provide you with a model name for your small ship, but not a name for individual ships. This system is modeled off of real-world military naming conventions.

(6)(3)(2)(1) - (4)(5)

This is an optional component which may or may not apply. Select the applicable designator (if any) and place the letter in position (1).
D - Drone Controller
Q - Drone Fighter or Weapon
S - Spaceplane (capable of both atmospheric and space flight)

Select the description which best describes your ship's purpose when you designed it. This letter will be placed in position (2).
B - Bomber
C - Cargo
F - Fighter
H - Search & Rescue
K - Tanker (Battery Recharge ship perhaps)
M - Multirole craft (designed to perform 3 or more of these roles)
R - Reconnaissance
U - Utility (Driller, Welder, Grinder, etc.)

For designs which you have modified to serve a secondary or additional role, and place that letter in position (3). This is to be applied to some base ship to which you have added a new feature. For example, if you had a Fighter (F-01) which you added a a Remote Control to you would classify the new variant as QF-01. However, if you built the ship as a drone fighter from the start (with no cockpit) then it would have been classified as FQ-01 already and you would skip this step.
C - Cargo
F - Fighter
K - Tanker (Battery Recharge ship perhaps)
M - Multirole craft (designed to perform 3 or more of these roles)
Q - Drone Fighter or Weapon
R - Reconnaissance
U - Utility (Driller, Welder, Grinder, etc.)

For vessels you would like to classify as experimental, place an X in position (6). If your ship is not intended to have any mission or variant mission, then it might only have the letter X on the left side of the hyphen.
X - Experimental Design

Position (4) is just a sequential numbering slot. Your first Fighter (F) is F-01. Your second is F-02. If you modified your second fighter to include a Remote Control block, then it would be QF-02 as it is still the same design but with a Variant mission assigned. However, your first DRONE Fighter would be FQ-01 as it is a different type of ship entirely.

Position (5) is used for letters which designate upgrades to your designs. The letters "I" and "O" are skipped to avoid confusion with 1 and 0. If you're just modifying or updating your F-01 to include new or alternate weapons, then you would not classify the revised ship as an F-02. You would classify it as an F-01A.

source - Understanding US Military Aircraft Designations[www.wikihow.com]

Large ships are defined by a class, serial number, and ship name.

A ship's class will be one of the classes listed below, or some subclass or variant. Each class has a 2 or 3 letter code (PC, FF, CL, CVE, BC, etc). A ship receives one of these codes combined with a serial number. For example, if it is the 5th heavy cruiser a navy has built, then it would be CA-5. This covers the alphanumeric component. A ship name consists of a prefix followed by the ship's name. In military ships, this prefix often relates to the national allegiance of a vessel. For example, ships belonging to the British or some Commonwealth nations are referred to with the H.M.S. (Her/His Majesty's Ship) prefix while the United States uses U.S.S. (United States Ship). The Terran Star Navy uses the prefix T.C.S. (Terran Commonwealth Ship).

If you would like a way to tell Atmospheric ships apart from Space-worthy ships, just add "S" to the front of any designation used for spaceships. So a Space Carrier would be SCV.

Many of the naval hull classifications were derived from reviewing lists like this one:

source - Hull Classification Symbol[en.wikipedia.org]

Civilian, or merchant ships, use prefixes which refer to the ship's function.

source - Ship Prefixes[en.wikipedia.org]

With the addition of planets, there is now the option to build ships that are exclusively atmospheric!
The guide as-written so far is intended to apply to space-faring ships. I will be adding "S" to the beginning of all my ships intended for space flight (SCV, SBB, SDD) and using the standard designations for atmospheric craft.

Additional letters can be added to a hull classification to represent variant roles:
C - Command: Denotes a ship of medium size or larger with expanded communications or command-and-control systems. I can't say I know what you'd use this for in S.E. specifically (Maybe a laser antenna hub ship?), but it might come up!
Examples: CLC, DDC, CC*, CBC, CVC

G - Guided Missile: Most ships of escort size or larger equipped with, or modified to carry, player-made missile weapons would fit with this designation.
Examples: FFG, DLG, CLG, DDG, CG*, CBG, BBG

M - Minelayer: Ships designed to deploy minefields. These are either medium (DM) or large (CM) ship hulls, as they're made from Destroyers or Heavy Cruisers.

N - Nuclear: Denotes any ship whose power source is nuclear. This is the last letter in any classification. For example, if you have an Aircraft Carrier (CV) that's exclusive to space (SCV), a command ship (SCVC), and nuclear the symbol would be SCVCN. I've excluded N from my classifications because I assume all my S.E. designs are nuclear. This may be relevant to folks running mods or alternate fuel for their ships.

R - Radar: Denotes a ship of medium size or smaller with a focus on scouting and Radar detection systems (a Radar picket). Like the Command designator, I'm not certain how you'd use this in S.E. (maybe some scripts that detect debris or ships that aren't broadcasting?), but it's an option!
Examples: DER, FFR, DLR, CLR, DDR

S - Scout: Used briefly for the concept of a "Scout Cruiser" (CS*) and again for a "Strike Cruiser" (CSGN). Recommended simply because having a Strike Cruiser designation sounds too fun. So it's a faster Heavy Cruiser. Similar to the difference between Battleship and Diet Battleship (Battlecruiser). Slimmed down armor to make it lighter. The weight difference then is either applied to thrust to make it faster or guided missile weapon systems to give it a longer-range strike capability. Just sayin, but a Heavy Cruiser that's had a ton of armor stripped off to install hydrogen-based boosters for sudden acceleration? Sounds really cool.

*You may have noticed a distinct lack of Heavy Cruiser (CA*) variants. That's because when assigning a classification symbol to a Heavy Cruiser, the "A" is dropped and replaced by the variant letter. A Heavy Cruiser (Command) isn't CAC, it's CC. A Heavy Cruiser (Guided Missile) isn't CAG, it's just CG. A nuclear-powered Heavy Cruiser would just be CN, however if it has any other variants the N will be added after them (i.e. CCN or CGN)

Since only seeing my personal build style for ships wouldn't really express the wide range each class might contain, I've started checking the workshop for quality Vanilla builds that fit some of the class descriptions I've set up in this guide.

In selecting these example ships, I often find a design fits very well in one of the classes described in this guide whereas the creator has assigned it a name matching another class present in the guide. This is a thing that happens in real life, too. One navy builds a ship and says "This is an escort!" Meanwhile, one of their rivals might look at it and go "...that's definitely a frigate."

This guide is FLUFF for my fictional Terran Star Navy. It's meant to inspire others in their own builds and offer suggestions if you're not sure how to classify a ship. Other builders are not wrong to classify ships differently. When you see someone's destroyer in this guide under "frigate", consider that the assessment of TSN admiralty as they compare the ships of other navies to their own fleet.

Strange word? The littoral zone is a region of water close to the shore (as opposed to open ocean). In the context of Space Engineers, I have commandeered the word to use it in reference to smaller ships that are designed to operate close to their home bases. It's not an entirely accurate representation of the real-world classification systems, but that's not what this guide is about. It's an adaptation and I needed to co-opt terms for this system that make sense.

Littoral ships in Space Engineers are distinguished from larger vessels by their lack of support systems (Medical Rooms & Cryo Chambers) and their inability to travel long distances (no Jump Drive). They operate from nearby bases or from a ship dedicated to their maintenance and transport.

0 - 1 layers of Heavy Armor
0 - 4 Turrets
0 - 4 Rocket Launchers
Under 1,000,000kg

Minimum Acceleration: 14.0 m/s/s
The emphasis in these ships is on speed, Rocket Launchers, and Missile Turrets.
Example:
x
Take some custom-built weapon system (like a gravity cannon), then build as small of a ship around it as you can to make it mobile. You've now created a Gunboat. Gunboats are mobile weapons platforms, useful for bombardment of space stations.
Example:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1516818880
Mass: 400,000kg - 1,000,000kg
Like a smaller Frigate. Well-armored with well-rounded weapons.
Example:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1433518542
A small ship built to transport and fire player-constructed torpedoes. A means of carrying small numbers of heavy weapons for deployment against larger targets.
Example:
x

Escort Vessels are the smallest class of ships in a navy capable of independent operations. When I say capable... I mean my Toyota Echo is capable of carrying 6 people. That doesn't mean I want to do it for very long. Escort Vessels have at minimum a Medical Room, but do not necessarily have the space to provide full pressurization systems as seen in larger ships (meaning, they have air but not every doorway is an airlock). Escorts often serve to fill a role in a larger fleet. Corvettes act as scouts, Escorts provide defense against missiles and fighters, and Frigates serve as lightweight combatants to counter other Escort or Littoral combat ships.

These ships are larger than Littoral ships. Escorts are designed to travel with the larger vessels that they are supporting, and so must have a Jump Drive in order to follow the fleet.

0 - ½ layers of Heavy Armor
2 - 6 Turrets
0 - 6 Rocket Launchers
1 Medical Room (minimum)
1 Oxygen Tank (minimum)
1 Cryochamber per crew member
1 Jump Drive (minimum)

Mass: 500,000kg - 800,000kg
A small ship built with an emphasis on Gatling weapons (missile weapons optional). Serves as an anti-fighter/anti-missile defense screen for larger ships. Cheap & expendable, escorts are designed to protect more valuable assets (capital ships or space stations). Escorts only need to be as fast as, or slightly faster than, the capital ships they're assigned to protect.
Example:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1411187935
Mass: 600,000kg - 1,000,000kg
Minimum Acceleration: 14.0 m/s/s
Lightly armed & armored vessel which is fast and makes use of Rocket Launchers.
Example:
The weapons on my Warhawk don't exactly reflect the class description, but the ship's high speed and relatively low mass are what define the class.
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1408440001
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1131586577
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1414729415

Mass: 800,000kg - 2,000,000kg
Heaviest of the small ships, greater focus on armor and turreted weapon systems.
Example:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=636918656
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=807223615

½ - 1 layers of Heavy Armor
6 - 12 Turrets
0 - 15 Rocket Launchers
1 Medical Room (minimum)
1 Cryochamber per crew member
1 Oxygen Generator, Oxygen Tank, & Air Vent (minimum)
1 Jump Drive (minimum)

Medium ships are the first category of ship intended to be fully capable of long-range autonomous operations. For this reason, they should all possess a Jump Drive and a pressurized environment.

Mass: 2,000,000kg - 5,000,000kg
DL, or Destroyer Leader, is a hold-over from America's naval designations from World War II, where American Destroyers were comparable to the Frigates of other navies. Many enlisted personnel in the Terran Star Navy refer to these ships as "Light Destroyers". Although not technically accurate, it does describe the Heavy Frigate's role in the Terran Star Navy.
This is the lightest vessel in the medium ship category, often these are up-armored frigates.
Example:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1246039684
Mass: 4,000,000kg - 6,000,000kg
A fast & maneuverable ship-to-ship combatant, intended to protect capital ships against smaller vessels.
Example:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1430358362
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1357279737
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1386188210
Mass: 5,000,000kg - 7,000,000kg
A moderately armored ship intended to engage other medium ships. The lightest ship classification likely to mount a player-designed turret system. Unlike Destroyers, which are often focused combatants, Light Cruisers are more well-rounded in their construction and fields of fire.
Example:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=642319187
Mass: kg - kg
Compliment: 0 - 3 Fighters
Minimum Jump Distance: 4,000km
A lightly armored ship with long-range scouting and first strike capabilities. Strike Cruisers can serve as a command ship for task forces of smaller attack craft. Ships of this class need extended jump capabilities so they can travel ahead of the main fleet more easily.
Example:
x

Mass: kg - kg
Compliment: 4 - 6 Fighters
In real life, there's not much distinction between an Escort and Light Carrier. But when I realized I could rework my Light Cruiser into a carrier, I decided I needed to split the terms. Historically, many Escort/Light Carriers were repurposed freighters or cruisers converted to the task. During WWII, naval personnel made the joke that CVE stood for "Combustible, Vulnerable, & Expendable." In order to carry fighters (and the fuel & ammo they used) these ships had far less armor than vessels of comparable size. A CVE has thin armor wrapped around large caches of ammo and fuel. They have few defensive armaments and are slow-moving.
Example:
x

1 layer of Heavy Armor
8 - 20 Turrets
0 - 30 Rocket Launchers
1 Medical Room (minimum)
1 Cryochamber per crew member
1 Oxygen Generator, Oxygen Tank, & Air Vent (minimum)
1 Jump Drive (minimum)

Mass: kg - kg
Compliment: 6 - 10 Fighters
CVLs are support ships meant to stay behind the lines and provide local fighter support for other ships and outposts. They're self-sufficient but require protection, and they can serve as command and control ships if necessary.
Example:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=678861220&tscn=1537003951
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1416449488

Mass: 7,000,000kg - 10,000,000kg
Larger than a Light Cruiser with more armor and weapons. Intended to combat other medium and large ships. Likely to have at least one player-operated turret or other heavy weapon system.
Example:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1521553754

1½ - 3 layers of Heavy Armor
Lots of Turrets
1 Medical Room (Minimum)
1 Cryochamber per crew member
2 Oxygen Generators, Oxygen Tanks, & Air Vents (minimum)
1 Jump Drive (minimum)

Mass: 9,000,000kg - 12,000,000kg
Nearly Battleship-sized cruiser-killers with lighter armor to keep up with their smaller quarry while still carrying as many weapons as a battleship.
Example:
x
Mass: 10,000,000kg - 14,000,000kg
The epitome of naval combat. The largest of any of the ship classes, covered in extensive armor and many of the heaviest weapons available. The only thing that threatens a Battleship is ANOTHER Battleship, and that's what they're built to fight.
Example:
x
Mass:
A battleship-sized vessel armed predominantly with anti-aircraft weapons, designed with extensive resupply and storage capabilities.
Example:
x