A/N - So you can rename armies. Barely worth the effort, because all you really do is amass 'em, throw 'em into the grinder. And if you want to keep the themes going, you need to keep checking the army lists after every invasion. So even though I initially renamed them at first, I kinda gave up after a while. Doesn't mean I didn't create backstories, though. And with the leak that Modern Warfare is 4-less, let's check out some USGSFs.
GSF-01A "White Star"
The Paragon
Symbology - White star in a white circle on an army green backdrop
If there was a meter that measured pride, then those that are able to make it into White Star would have broken it long ago. Then did another pass over to break it three more times while they were at it. The very first GSF, every effort was made to do things "right". Every soldier here is propaganda poster worthy, and every word in the book of war written by this Strike Force is followed to the letter. And even when they have to deviate from the book, they try to do so in the best possible way. Excellence isn't just something they strive for, it's an essential imperative running through the very fibers of their Meld cores.
Of course, this strict high standard has led to many outsiders finding them
kinda on the elitist snob side. An image not helped by the rather stiff outward personality they tend to portray. Which isn't to say that they are completely humorless. It's just that it tends to be a rather dry, understated humor told absolutely deadpan.
And then there's the milspeak. If most GSFs tend to lay the jargon on thick, then White Star is fortress wall worthy, to the point that even other units don't always know what the heck the White Star is saying.
That said, anyone who's able to find an entrance into their tightly knit circle of friends will soon learn that a White Star is truly the best person to have by your side. Fiercely loyal to each other, their own beliefs, and to their nation, in that order, a White Star is truly unshakable in the fight for liberty and justice, no matter if their opponent is foreign, or domestic. They truly are the white knights of the US military.
Doctrines - As those who believe they are the standard, White Stars are trained in everything in preparation for anything. Every army's got that "Jack of all trades" that is balanced in a wide spread of tactics. White Star's essentially that, capable of adapting to any situation as is needed. With one notable exception. Or notable reinforcement...
Unique Units
Warfighter - If a White Star is capable of fighting in every possible scenario, then a White Star Warfighter is
the best at fighting in every scenario at once. The pinnacle of the Strike Forces doctrine of Full Spectrum Warfare, clothed in experimental power armor with
every gadget possible, armed with the most tacti-cool weapons known to man, skilled in every
other type of weapon discovered or otherwise, and ace pilots for every type of propulsion available to any military force in the galaxy, the White Star Warfighter is, simply, and army of one, and an army of all.
A/N- Because the reference is so niche, I'm just going to explain it here: In Marvel Ultimate Alliance 2, the SHIELD agents that defect to Captain America's side call themselves "White Star" out of respect for him. Kinda hoped they would bring that back after MCU's Winter Soldier, but eh, what can you do? Well, besides make up an army for a sci-fi setting. 
GSF-01M "Dire Devildogs"
Semper Fidelis est in spatio
Symbology - Stylized Marine Corp Logo
At the birth of the USNA's Stellar Age, it was only natural that the Navy take over as the military branch in charge of outer space operations. While the Air Force tried to use it's connection to NASA as leverage, ultimately they didn't have the same history of stuffing large groups of people into isolated cans in the middle of a hostile environments for extended periods of time as the old boat-sailors did. And anywhere the Navy went, the United States Marine Corp were sure to follow in its wake. Once more primarily focused on ship security and boarding actions, in the early days it was becoming increasingly uncommon for a Jarhead to even be deployed planetside. As warfare started to crop it's ugly head back up, however, and CENTRALCOM started needing to recruit off-world assault armies, once more the USMC rose to the call.
That said, once more the Marine's position as a sub-branch of the Navy limited them. While not unheard of, rarely was an entire assault army made of Marines. Usually they were deployed as a supporting division in a larger force reporting to the Army, and sometimes it wouldn't be to the same force from drop to drop. Marines adapt, though, and were more than capable of rising to the challenges.
When the GSFs were created, all of that changed. Like the JSF from before, the GSF was based on the Marine Corp structure, with many of its practices ("Every man a rifleman" for instance) being the core building blocks for what was developed. So naturally, many of the best GSF recruits happened to be Marines. However, in many cases this meant that Marines were spread out amongst the other GSFs.
General Alexander Graham Hamilton IV had other ideas.
A seasoned veteran of the Corp, General Hamilton took the opportunity to take over the recruitment of GSF-Mike with the aim of recruiting a pure Marine force. He made this goal absolutely clear when naming the Strike Force "Dire Devildogs" from the very start. And he would rankle a few chains along the way, practically stealing some recruits out from under the nose of other GSFs, as well has heavily modifying the training procedures to be more in line with a heavy Marine-colored point of view.
No one could argue with the results. As the Dire Devildogs were amongst the first GSFs deployed, they would gain a reputation out in the field in a way that only Marines could get: Rough, hardened, highly motivated, surprisingly resourceful... and as always, completely, unshakably, faithful.
Doctrines - The doctrines of the Dire Devildogs is that of the very core of the Marine Corp, and therefore the GSF, though their background as a Navy sub-branch has colored their approach somewhat. While the White Stars, for instance, embrace the new warfighting technology provided by the program, GSF-M is full of people more used to a sparse supply line.
As a result, the Strike Force tends to prioritize training above fancy gear. "Dire Devildogs go bareback" is the rather colorful saying about them, as they often can be spotted by their rather Spartan appearance in comparison to other Gene Warriors, such as using basic sights instead of scopes on guns, or armor that's sometimes stripped of secondary features deemed unnecessary.
In addition, Dire Devildogs take the "Marine=Rifleman" saying very seriously, and as such often base their tactics around that, either attaching more specialized units to a Rifleman squad, or splitting Rifleman fireteams to attach to specialists.
Unique Units
Scout Sniper - Marines have a long history of making some of the finest snipers in the human sphere, so naturally Dire Devildogs take pride in their Pathfinder units. Scout Snipers, in particular, have honed their skills to a fine edge, something made even more impressive by their use of much more old-fashioned techniques. It is usually a bragging point that they don't rely on battery-powered optic cloaks or high-end scopes to accomplish their missions, instead using classic ghillie camo and head calculations. Some do point out that the "ghillie suits" use high grade mold materials instead of salvaged foliage, and the "low end scopes" they do "head calculations" with still have rudimentary distance calculation algorithm displays, aka they still use calculators for their math. You still wouldn't want a Scout Sniper hunting you down, though.
Leatherneck - "4 Gauge Brawling" is a GSF variation of "12 Gauge Brawling" in reference to how much more powerful the shotguns used by Gene Warriors tend to be in comparison to regular shell blasters, even if the classic gauge measure isn't
technically true anymore. Compared to other gun-fus, though, it really is a rugged brawling style, something which fits in perfectly with the Marines of GSF-01M. In particular is the use of pump-action techniques, both for its greater reliability over auto-shot, and it's ability to swap between different munitions. Leathernecks are experts in this latter area, in fact. Veterans are even said to be able to clear a whole room using only a single magazine of pre-planned shells, including the door breach, as well as different ammo for differing ranges. If nothing else, they are very good at getting the gun to *KA-CHAK* just so.
Force Recon - An elite variation of Riflemen, Dire Devildog Force Recon are often deployed at the tip of the spear of any assault, and are usually found where the firefight is thickest. They also are even better at making use of specialist attachments, as many have had training as such units by the time they qualify for these squads.
Jarhead - A sort of final say about the age-old Marine nickname, the Jarhead is called that due to the one fancy gadget that the Strike Force actually makes use of: the Smart-Link Helmet. Often used in conjunction with the "third arm" gun brace, the SLH is able to accommodate a wide range of heavy automatic weapons, allowing the Jarhead to lay down highly accurate fire on anyone they can lock onto. Useful as it is, it can be a bit tricky to use, and in some cases units have been known to "unscrew the cap" during a fight to aim manually. Still, it doesn't show signs of going away any time soon.
Busdrivers - A rather cheeky nickname given to some Dire Devildog pilots due to the special field modifications they make to their vehicles. As the Strike Force's doctrine makes heavy use of attaching rifleman fireteams to other units (or other units to squads) it is not uncommon for combat vehicles to have a few troops supporting them. A few of these take that to the next level, and have seats to allow Marines to ride on them. The two most famous examples being the "Slinged" Arrowhead Attack VTOL letting a fireteam hang from the sides, and the "Bunker Hill" Washington Master Battletank with special treads allowing a squad of infantry to sit on top. Admittedly this practice can be fairly risky for the troops, but many Dire Devildogs are having too much fun to care.
What is next? Not sure myself at the moment.
