A few things that came to my mind:

I think you may be thinking to broad in your conceptualization of aggression. Especially if you are trying to include things like decisiveness or readiness to take action, which may not be included or even addressed in an aggression scale. The term "aggression" is massive in IO. Keep in mind that "workplace aggression" is currently comprised of about 5 general sub-fields (Bullying, interpersonal conflict, incivility, abusive supervision, and bullying; Herschovis, 2011), so i am not sure if that is what you are looking for.

ROTC =/= the military so there may be some issues with making generalizations.

Psycinfo, google scholar (especially when you are logged in through an on campus account with access to the library), and your current psych teachers/ whoever you are interning for/ whoever you are doing research with are all AMAZING resources.

You may want to look at trait anger (Spielberger, Jacobs, Russell, & Crane, 1983; this is one of the earlier citations) as there may be some overlap.

You are going to have a hard time linking current "aggression" measures to actual military performance as ROTC is not actual military performance, and unless you are going to be able to follow up with the people in a few years AND get access to there performance evaluations it will be very hard to do what you want.

What you can do is demonstrate the relationship between "aggression" and success at their ROTC jobs. Specifically, if you can link "aggression" to a stronger ROTC performance and then show how a stronger ROTC performance is linked to a stronger military performance you got yourself a stew going.

Feel free to disregard this paragraph if you are not going to publish or present these findings in any professional manner: Keep in mind, if you start pulling data with the end goal of getting it published (or even into most conferences) you are going to need to do an IRB. If you don't know what an IRB is, you need to go talk to a psych faculty member. If you do know what it is, then you probably already know you are going to need a faculty member to sign off on it.

It is good to see you thinking about this type of stuff early on in your career as a student. Check out http://ipip.ori.org/ for a great list of open source psych scales. It may give you a better sense for how psychological constructs are broken down.

Also, if you are thinking about grad school and are not currently doing research with a prof or in a lab I would recommend that you try to get into one asap, for a number of reasons.

Finally, read Thesis and Dissertations on subjects you are trying to understand. They usually do a better job explaining the history of the various constructs and variables that they are using (more consistent anyways).

If you don't know how to pull research (articles, dissertations, ect) go to your library asap. Most college libraries offer solid beginner research courses that take maybe an hour of your time.

TL/DR: Good thinking, but may be a bit to big. As you are learning your way start small, think slowly, and try and find someone smarter than you who can guide you 1st hand.

edit: words and spelling are hard :P