> But as a civilian, I'm not sure why I'd give a shit.

I hope you give a shit about the effectiveness of theprotection others are delivering you. The sort of person who works well in the Air Force is not the same sort of person who works well in the Army is not the same sort of person who works well in the Navy is not the same sort of person who works well in the Marine Corps. The jobs of the services are fundamentally different, as are the mindsets & aptitudes of those in them.

The Air Force is a mid-century corporation: it has metrics and deliverables (literal deliverables), and is oriented towards long-term sustainment of whatever it is asked to do. It's very, very good at building an organisation to do the same thing for years, with good morale for its people because they are never tasked too hard, and excellent safety results because that's important when operation a mid-century concern. On the downside, most of it is not really all that flexible, and its culture is not, in the main, oriented towards enduring long-term suffering (there are exceptions). If you have something you want done, you ask the Air Force. If you ask an Air Force officer to secure a building, he'll buy it.

The Army is big. Really big. You just won't believe how vastly, hugely, mindbogglingly big it is. It's all about mass, directed according to very strict orders. If you need to pave 1,000 miles of road, the Army Corps of Engineers will do it, according to its plans. If you need to garrison a town, the Army will do it, all nicely and neatly and according to plan. If you have a problem someone's faced before, you want the Army. There's a field manual for everything: a field manual for improvised munitions (because of course there's a manual for improvisation), a field manual for executions, a field manual for skiing. If you ask an Army officer to secure a building, he'll surround it and not let anyone in or out without authorisation.

The Navy is a floating, violent industrial plant. It never does the same thing twice; it's always going to one new port or another. It's not as laid-back as the Air Force, nor as regulation-bound as the Army. It speaks an entirely different dialect of the English language, for no particularly obvious reason. If you have a problem that no-one has ever seen before, you ask the Navy for a solution. If you ask a Naval officer to secure a building, he'll make sure a sailor sweeps & swabs the decks, and puts out the lights.

The Marines are a cult. They worship at the shrines of Chesty Puller, Dan Daly, Smedley Butler & John Basilone. They think that war is a racket, but they don't particularly care: they enjoy the racket. If you absolutely, positively need it dead or destroyed within 24 hours or less, you call the Marine Corps. If you ask a Marine to secure a building, he will take it by force, killing or capturing everyone inside. If he does a particularly good job of it, he'll be deified and join the pantheon along Puller &c.

If you put someone well-suited to the Marine Corps in the Air Force, he'll be fired for getting into a little trouble on the weekends. If you put someone well-suited to the Navy in the Army, he'll go out of his mind from boredom. If you put someone well-suited to the Air Force in the Army, he'll be miserable and quit. If you put someone well-suited to the Army in the Navy, he'll just be generally appalled.

The different services have different roles, different strengths and different weaknesses. Those differences are why they are well-prepared for a major conflict.