@Mushroom
I will be honest, one author I love but will not name is pretty antagonistic to the military. And in one story he stated over and over you sign the contract, then take the test. So you may get stuck with a job you hate. SO in other words do not join the military.
That is wrong, it is the exact opposite. And it always had been. I understand taking "artistic license", I do it a lot. Occasionally place in something anachronistic say for story reasons, but when they write completely wrong out of laziness, I tend to move on.
Depending on time frame, he could be right, or partially so, even now. IIRC, the current paradigm regarding the ASVAB didn't exist until outcry over the [i]recruiting[/i] of the mentally handicapped to fight in Vietnam. Which is where they began to be required to test first, and anybody in the bottom quintile was disqualified outright, the next 10% or so was "negotiable" depending on various factors. (20 years ago, the cutoff for all branches was at the 30% percentile for intelligence, but a couple branches could get waivers for as low as the 27th)
Yes, the current paradigm is test enlistees to verify they're "capable" of performing the job they're signing up for, and they attempt to schedule them to ensure that is what they get.
But there were, and probably still are disclaimers attached to those contracts. If your personal training gets delayed for any reason(for example an illness or injury during bootcamp which causes you to be set back in training) and that spot you signed up for, and were scheduled to be trained for goes away. At which point you're entirely at the mercy of "the needs of the military (branch)" and what they have available to you. Or in other words, "Sign the contract, then we'll tell you what you're going to get."
Of course, the military hates it when things go off-track, so they'll generally move heaven and earth to put things "back on track" before it reaches that point, but sometimes, it just cannot be helped.
The military changed a lot between the 1970's and when I got out, I imagine it has changed more since then, but probably not as much as it did going from say 1970 to 1998(and Tailhook in particular).
The all volunteer force, the 24/7 news cycle just itching for a public scandal to obsess over, and modern communications connectivity makes for a very different realm than the draft-era force that could do pretty much whatever it wanted(within certain, very widely and vaguely defined bounds) with minimal concern about what was going to be heard about back home.
But then you have things like Vet TV kicking around to (allegedly) demonstrate just how different things are from how many (post 9/11) vets view things and how the wider population views the military.