The Squad

"Look, we know you're new to this command, but the army field manual is very clear on the subject of squad stereotype composition. Every squad must include: 1 quiet religious guy who goes insane, 1 maverick loose cannon who plays by his own rules and dies in a blaze of glory, 1 covert recon opperative with a dark past who at first betrays the team but then has a last minute crisis of conscience and nobly sacrifices himself for the greater good, 1 fresh faced new recruit who survives but loses his innocence and learns to become a man and 3 or 4 other guys who you don't care about so they can get brutally shot so you can show how serious the war is."
Loading Ready Run makes it official.

Military and war stories have a number of different levels of focus, from the global strategic level all the way down to squad tactics, and even the plights of individual soldiers on the battleground.

When the focus is at the smaller end of the scale, we get this trope. Very often, this is a squad composed (like a Five-Man Band or The Team) of interlocking character types or roles.

There are quite a few similarities with the types and roles of the Command Roster. The main difference is the Command Roster is a very specific combination of skills that may not be strictly military. The Squad may be a Badass Crew and have a Squad Nickname. If it's made up of women, it's an example of an Amazon Brigade.

The trope's inspiration comes from the fireteam and squad units of infantrymen used by militaries to this day. Possibly first appearing in The Napoleonic Wars where open order skirmishers armed with rifles at the time more accurate but slower to reload than standard muskets would depend on coordination for them to stealthily get into position for a good shot and minimize exposure to the weight of fire of much larger densely-formed musket-wielding line infantry units that were around the battlefield, the concept was codified in World War 1 where breech-loading rifles using smokeless powder (gunpowder in The Napoleonic Wars was black powder that would quickly fill the area around a shooter firing repeatedly with thick smoke that would render firing accurately improbable) had become commonplace to render the average infantryman much more potentially accurate and quick-firing than he was before (let alone the proliferation of machine gun crews) which granted a huge advantage to defenders in cover that would inevitably shoot first when a mass of men approached them. Military science thus experimented with infantrymen attacking fortified positions by approaching with methodical covertness in significantly smaller groups to avoid troops being quickly mostly killed at first contact from being in a large gathering until the concept eventually became the infantry's default grouping at the smallest level.

Some of those character types and roles:

If the story follows the characters through boot camp, or specialized training, expect to see Drill Sergeant Nasty make an appearance. If the story follows them after the war, expect at least one Shell-Shocked Veteran.
Some works featuring The Squad include: