Naval and Land Forces
Space Combat
For most instances, space combat is similar to oceanic naval combat that pre-spaceflight races have certainly waged; the concepts have not changed much overall. In broad senses, garden worlds are the ports and islands of this era, space is the endless black sea, and mass relays are a facsimile of nautical lanes and canals. Species that ruled the seas with battleships now rule the space with dreadnoughts; stealth vessels are akin to the roles submarines performed before. Instead of radars and satellite imagery, spaceships have sensors and special extrapolation data - pursuers cannot detect ships and directly intercept them, instead, pursuers track where objects were, where they were heading, and at what speed they were moving. Such data reliably predicts an object's future location and for pursuit along its light-lagged "wake".
To understand naval combat tactics, firstly we shall need to learn about naval vessels. Although many types exist, and each race fields something unique and specific to their combat style, there are four types of starships in military sense. The first three, namely dreadnoughts, cruisers and frigates are pretty similar across all navies; the fourth – crossovers – vary wildly. The dreadnought, which is a kilometer-long titan with a main gun almost the same length; is dedicated to the projection of firepower and leading a fleet. The cruiser, which can be of many types, is the standard unit and the bread and butter for most navies, save some. The frigate, which is the light scouting element, equipped with powerful drives and guns, experimental and specific-use missiles and torpedoes etc.; focused on slipping through the enemies' defenses and landing critical hits. Smaller crafts like boats, sloops and corvettes are used in patrol and system defense roles.
Lastly, the crossovers are amalgamations of the three previously stated ship types, like the carrier, the battlecruiser, the destroyer and the prowler. They vary among species and their mindset towards combat. The carrier, which is a human design, focuses on utilizing fighters, bombers and fast-attack crafts (sloops and boats) as main weapons. The battlecruiser and the destroyer, both developed by the Hierarchy, are used to bridge gaps; between cruisers and frigates for destroyers and between dreadnoughts and cruisers for battlecruisers, with more endurance and firepower in a compromised package. The prowler, a salarian design, is a small, stealthy warship, the size of a corvette but carrying firepower on the level of frigates; used for deep strikes and infil/exfil missions akin to oceanic submarines. There is also the sloop, a Migrant Fleet concept – ships barely larger than boats, often VI-driven or remotely piloted; loaded with GARDIAN, missiles and torpedoes. Used in very large numbers to overwhelm the enemies' larger ships, leveling the playing field against an enemy with superior firepower.
The doctrine of naval combat can be gleaned from what kinds of warships a certain navy uses. For example, the Hierarchy navy focuses on frontal attacks and fleet formation combat; and as a result, the Hierarchy navy features dreadnoughts, cruisers and destroyers heavily, with a lesser focus on frigates and smaller ships. The asari, with their evade, tire and decapitate maneuvers; focus on light cruisers and heavy frigates empowered by the feared Destiny-class dreadnoughts. Salarians with their obsession of cutting-edge, diversion and stealth, use battlecruisers and heavy cruisers flanked by frigates and prowlers; opening angles for their stealth dreadnoughts to emerge and one-shot the enemy capital ships. Humans rely on their carriers to disrupt any fixed formations and strategies (especially ours), while using their dreadnoughts and cruisers in formation combat and the frigates and destroyers as flanking, wolf pack flotillas. Quarians, with their sloop concept, utilize very large numbers of sloops and other fast-attack crafts (under the command of the patrol fleet), to overwhelm the enemies' larger vessels, while their frigates and destroyers close in to deploy extensive ECM and cyberwarfare measures against the capital ships.
Planetary and Land Combat
Planetary combat is divided into two aspects – space superiority and terrain control. Successful assaults on garden worlds hinge upon up-to-date intelligence. Attackers need to determine where the enemy's defenses are, so they may approach from an angle that allows them to fire without ruining the resources below. Once control of orbit has been lost, defensive garrisons disperse into the wilderness. An enemy with orbital superiority can bombard surface forces with impunity. The best option for defenders is to hide and collect reconnaissance in anticipation of relief forces. Given the size of a planet, it is impractical to garrison entire conquered worlds. Fortunately, colonization efforts tend to focus on building up a dozen or fewer areas. An invading force relies on efficient deployment measures and their marine forces to be deployed directly from space in pathfinder maneuvers, establishing a beachhead for other forces to land. These ground forces occupy the spaceports, industrial facilities, and major population centers.
As a rule of thumb, every species have their defenses focused - he who tries to save everything, loses everything. Heavily defended worlds tend to be either Homeworlds, the planet of origin of the race; or strategically important planets, as we like to call them - Fortress Worlds. Homeworlds, in most cases, have the largest population by a solid margin (only exceptions are krogan and batarians) and are most protected. Fortress Worlds lie in convenient distance from mass relay nexuses and/or important space stations, and host a large number of fleets and soldiers.
Some races, for example - the humans, have a distinction between defensive garrison forces stationed on protected worlds, and expeditionary forces used in disputed and distant worlds. Due to the lack of dextro-based worlds, we do not have the luxury to spread our supply line across the stars this way. Our forces are concentrated on Palaven itself - and other important colonies, and we must rely on deep space stations and our valiant auxiliaries to transport us to the battlefield. Fortunately, no one else has a auxiliary and logistics like we do - so this is not much of a problem in the larger picture. We, for now, do not drive a schism between our forces by labelling them 'marines' or 'soldiers'. The only unit that can be labelled as garrison forces are the Raven Guard - who are entrusted with protecting major cities and Arcann relics on our worlds.
One other race that imitates us in this aspect are the quarians and geth - but that's because the Migrant Fleet Marines are small in numbers, and they aren't really thinking of colonizing or expansion yet. Geth don't require physical space to live, and sixteen million quarians can barely populate Siyyah, let alone the entirety of Rannoch.
Asari use this schism to maintain their subtle casteism. The Republican Guard (created by the Thirty) have the overall charge of protecting Thessia - all huntress units and commandos must cooperate with them if Thessia is under danger, ensuring no Republic gets too powerful. Other colonies are protected by their own huntress units and commandos.
The salarians do not have a concept of frontal war and they don't maintain any kind of standing army. The Union's armed forces are divided into two parts - the salarian navy and the STG. The STG takes care of ground combat - either by themselves or by hiring proxies, like using Gemini mercenaries for in-space dirty work, and raising batarians and drell as cannon fodders. Most garrison and defensive work is done by a gendarme force manned by the Six Families.
Human forces are peculiarly complex and over-compartmentalized. They have their UN watching over Earth, and the SolForce (officially called EDF) defending Earth and the Sol system. From what we understand, the Sol Force is a joint task force of Earth's richest and most powerful nations - evolved from a previous coalition called Nato. Outside of Sol, it's all Alliance - their Army protects fortress worlds like Terra Nova, Mindoir and Sparta, while their Marines are used to colonize and protect the Verge, the Traverse and edges of Terminus - wherever humans have a footprint. Regular marines and army are cut from the same cloth - if a bit mismatched in training and equipment; but the SolForce soldiers and top-rated marine frontier units are elite warriors, capable of handling their own alongside our best.
Land combat is the same as it has been since the discovery of spears - the force with the better knowledge of the terrain, better application of its abilities and better logistics usually wins. Every military wants to achieve these goals, but with varied approaches. Small-unit tactics are very diverse but in large-unit maneuvers, certain trends start to show among militaries. For instance, the Hierarchy's own tendencies are to deploy medium-sized elements augmented with special forces, air support and armor. The asari tend to use small hit-and-run commando attacks to bleed the enemy dry and then strike hard with Guard units. Salarians strike preemptively without warning and always try to maintain the best battlefield intel. Humans avoid direct confrontations with large enemy units, instead slip past the main lines and hit the supply lines and rear guard with special forces and light infantry units, and then cordon off the withering main forces. Batarians and krogan rely on horde tactics and attritional warfare.
Some common elements amongst all forces are visible. On attack, all races need a mixture of competent expeditionary forces capable of securing beachheads - special forces to hit hard targets, airmobile forces and orbital artillery to dissuade and pursue defenders, and air support to destroy strongpoints; in order to win. On defence, a deep and effective logistics system, a chain of strongholds and hiding spots, and a motivated infantry is required to drive off the attackers.
As per the Treaty of Farixen, this is the current known state of naval power of major races:
Power Blocs
Turian/Volus
Asari/Elcor
Salarian/Hanar
Human
Quarian-Geth
Terminus
Dreadnoughts
40 [+1]
21 [+1]
16 [+1]
11
4+3
0
Cruisers
812
542
496
172
112
Unknown [~500]
Carriers
1
2
0
6
0
0
Frigates
~1,200
~900
~500
~1,000
~400
Unknown [~600]
Auxiliary Fleet
~4,000
~1,500
~3,000
~2,000
~45,000
Unknown [~3,000]
Logistics Fleet
~10,000
~6,000
~2,000
~5,000
~200,000
Unknown [~8,000]
This is the current known state of land forces power of various races:
Power Blocs
Turian/Volus
Human
Asari/Elcor
Salarian/Drell/
Batarian
Quarian-Geth
Terminus
Krogan
Combat Personnel
40,000,000
10,000,000
4,000,000
2,000,000
[+150,000]
[+10,000,000]
2,000,000
20,000,000
[With PMCs]
50,000,000
Reserve
Forces
500,000,000
90,000,000
1,000,000,
000
Unknown, State Secret of the Union
Unknown
[Billions of Geth
Hardware in Storage]
Unknown
[Billions]
300,000,000
Support Personnel
100,000,000
35,000,000
20,000,000
10,000,000
Unknown
N/A
Unknown
Vehicles
15,000,000
5,000,000
4,000,000
10,000,000
~1,000,000
N/A
2,000,000
Aviation
300,000
80,000
100,000
150,000
50,000
N/A
N/A
Ratings including our own forces are as follows:
Turian Hierarchy – The most powerful military in the galaxy - OMEGA+
Systems Alliance – One of the most well-trained and professional militaries in the galaxy - OMEGA
Asari Republics - Second-most powerful navy in the galaxy, but weak land forces – OMEGA
Salarian Union – Very powerful navy with most cutting edge vehicles, but weak and unprofessional armed forces - OMEGA
Krogan Federation - Individually the best warriors, but not a competent formation force - DELTA
Rannoch Conclave – Largest flotilla in the galaxy with the most ship count, and one of the best infantries, but lacking in number - DELTA
Rachni Hive – Not ratable by conventional methods, going off of previous records - DELTA
Terminus Coalition -Motivated but unprofessional forces - DELTA
Courts of Dekuuna - Small but very well-trained forces - ALPHA
Illuminated Primacy of the Hanar and Drell – Decent navy along with the greatest specialists in the galaxy, small numbers - ALPHA
Vol Protectorate - Small forces, but very well-equipped - ALPHA
Batarian Hegemony – BETA
Vorcha – BETA
Confederacy of the Nemean Abyss – BETA