One of my favorite examples is that the first up-armored humvees for garrison patrols in Iraq were created by a National Guard unit. Simple part of the reason is that it had guys who as civilians were welders . . . so they tacked on some steel to the vehicle's frame.
Up-armoring equipment is as old as equipment itself. For years, archaeologists wondered why certain Roman helmets had a small visor that served no practical purpose. Surviving examples were found in Gaul and along Rome's German border. The visors weren't meant to shade the legionnaires' eyes, they served as a layer of extra armor, riveted in place, to ward of attacks by taller warriors, some with two-handed weapons not encountered on other frontiers.
A note on Humvee armor development: For years, the University of Hawaii was contracted to work on armor shielding at a remote island site in Kaneohe Bay. It was kept secret because many UH professors vigorously oppose
any form of research devoted to the US military, even medical. An inactive Marine (yes, there is no such thing as an ex-Marine...) friend told me great details about delivering sheets of metal, of various types, to the site and seeing the vehicles being modified. The UH doesn't work on anything that isn't being payed for, so grant money was coming from somewhere.
My question has never been "Why become a mercenary?" but "Why bother serving a House?" Mercenaries have far more leeway in choosing their opponents and locations, more freedom to develop their own doctrinal practices, all without swearing fealty to any of the corrupt empires that keep warring on each other. Fortunately, only one of the Houses had the giblets to stand up to mercenaries and end the practice of hiring heavily armed civilians to do government work. They even proved that they didn't need mercenaries to survive, but none of the other Houses were able to take that step.
As a GM, none of my players would ever consider being a regular. Sure, all of them served as regulars in character creation, but none of the sociopaths in my campaign fostered any loyalty to any House, and had no qualms about killing prisoners or civilians of their previous citizenship. When offered a chance to train at Outreach, my players unanimously refused any of the conditions required, the Star League was as dead as the Ares Conventions, so they formed a hiring hall and training cadre that competed with Outreach, and eventually surpassed them, by offering more than Outreach ever could: Legal defense, unit liability and loss insurance, guaranteed ransom payments, and a legal and military force capable of punishing any House for contract violations.
While Outreach was an exclusive, private club, the AoD (Army of *censored*) was all inclusive. They worked with the vast multitude of units that Outreach rejected or would never even consider. They even offered legal aid (and aliases) to units listed as pirates.
What could go wrong?
Half the nobles in the unit had their titles and holdings stripped away (they were warned) for atrocities on the field.
Several members had to be ransomed after being captured in an abortive assault against a well-defended facility.
One member was captured and beaten by Lyran police after a botched infiltration attempt (he was Black and the Lyrans could not tell him from a dozen mug shots of perps), so we was charged for several crimes he did not commit.
It went like this:
Detective Lang: So, Feldwebel (Sergeant) Johnson, I will call your unit HQ and talk to your superiors. I'll put the speaker on.
Johnson: It's late, so don't be surprised if nobody's there.
The phone rings in the unit office, the unit mascot, a donkey, ambles over to the phone and touches a button.
Donkey: Eeyaaw?
Detective Lang: Hallo? This is Detective Lang at the local precinct, we seem to have picked up a man claiming to be one of yours. Do you know a Feldwebel Johnson?
Donkey: Eeyaaw.
Johnson: (Whispering) Ugh, that's Oberleutnant Esel, he's just a jackass.
Detective Lang: You should be more respectful of your superiors, Feldwebel! So, Oberleutnant, do I hear a trace of Bavarian dialect? Perhaps Schwabian?
Donkey: Eeyaaw...
Detective Lang: It is so good to know that fellow Bavarians are serving as officers. I'll send your man back to you, if that is okay?
Donkey: Eeyaaw.
Detective Lang: I'll hang up now, tchuss! You, Feldwebel, are fortunate to serve under such a fine officer, I wish the Commonwealth had more like him.
Johnson: Trust me, the Commonwealth has an abundance of officers just like Oberleutnant Esel. One of the units appeared in a feature holovid that sparked a Capellan invasion of Carver V, on the rumor of a Star League base under a shopping mall.
...and fun was had by all...