Why is there a prominent cadet on Discovery?

Question

Why is Cadet Tilly on the U.S.S. Discovery?

This seems like an odd choice based on previous Star Trek precedent in general and also given that U.S.S. Discovery is the most advanced starship in the fleet in a time of war. Furthermore, it seems Cadet Tilly actually has a fairly prominent role on the ship.

As far as I recall, previously we only saw cadets at Starfleet Academy or acting under unusual rogue guidance in the case of Red Quad in DS9 "Homefront" and "Paradise Lost", not with a complete set of duties on an active starship.

Wouldn't the Tilly role fit better with some kind of enlisted rank, Non-Commissioned Officer, or Ensign ?

What is going on, both in- and out-of-universe?

Answer 1

In universe, she is probably another example of Lorca applying Regulation 139.82, allowing to conscript whatever talent he requires in a time of war. Tilly is brilliant and Lorca needs brilliance if Stamets' spore drive is ever going to work. It's always been bit fuzzy whether every cadet serves as a midshipman before graduation, but there's plenty of precedent for it in historical navies, and as one of the commenters mentions above, we know Kirk served as a midshipman himself (in the Prime Timeline; he never seems to have done so in the Kelvin Timeline).

Out of universe, she provides a counterpoint for Burnham. She's at an earlier stage on a journey Burnham has already been through--socially awkward for different reasons, still figuring out how to interact with a crew full of other people, optimistic where Burnham remains fatalistic in many ways. From a story-structure standpoint, Tilly is the Sidekick, loyal, supportive, helpful.

Answer 2

To clarify one matter: it is unknown whether Starfleet makes any distinction between cadets and midshipmen.

In English, cadet is a generic word for a person enrolled as an officer trainee in a national armed forces service academy. And it is also used more broadly.

Starfleet seems to be based on the mid-20th US Navy that was more or less familiar to the creators of TOS who supported it with their taxes and in some cases served in it. Midshipman is the official term for cadets at the US Naval Academy. A midshipman is simultaneously a cadet and a midshipman, whether in a classroom at Annapolis or on a summer cruise on a ship. An Annapolis cadet is not a midshipman only when on a summer cruise on a naval vessel, an Annapolis cadet is a midshipman all the time.

It is logical to assume that Starfleet is more or less like the contemporary US Navy except where there is evidence suggesting otherwise.

So what is said about cadets and midshipmen in TOS and the TOS movies? The following quotes are from the search function at Star Trek Transcripts site.

http://scriptsearch.dxdy.name/?page=index1

At the end of "The Cage" Pike says:

What are we running here, a cadet ship, Number One? Are we ready or not?

In "The Menagerie" they talk about Pike's injury:

MCCOY: What's his problem, Commodore?
MENDEZ: Inspection tour of a cadet vessel. Old Class J starship. One of the baffle plates ruptured.
MCCOY: The delta rays?
MENDEZ: He went in bringing out all those kids that were still alive. Just wanted you gentlemen to be prepared.

"Court Martial":

KIRK: Yes. He was an instructor at the Academy when I was a midshipman, but that didn't stand in the way of our beginning a close friendship. His daughter Jamie, who was here last night, was named after me.

"The Ultimate Computer":

SPOCK: Dunsel, Doctor, is a term used by midshipmen at Starfleet Academy. It refers to a part which serves no useful purpose. [now in "Kirk's quarters"]

"Whom Gods Destroy":

KIRK: When I was a cadet at the Academy, his exploits were required reading. He was one of my heroes. I'd like to see him.

and:

KIRK: I agree there was a time when war was necessary, and you were our greatest warrior. I studied your victory at Axanar when I was a cadet. In fact it's still required reading at the Academy.
GARTH: As well it should be.
KIRK: Very well. But my first visit to Axanar was as a new fledged cadet on a peace mission.

Star tek II: The Wrath of Khan:

SPOCK: Trainees ...to the briefing room.

and:

KIRK: Aren't you dead? I assume you are loitering here to learn what efficiency rating I plan to give your cadets.

and:

SPOCK: Welcome, Admiral. I think you know my trainee crew. Certainly they have come to know you.

and:

RESTON: Midshipman First Class Peter Preston, engineers mate, sir!
KIRK: First training voyage, Mister Preston?
PRESTON: Yes sir!

and:

KIRK: Well, Mister Scott, are your cadets capable of handling a minor training cruise?

and:

KIRK (OC): I told Starfleet all we had was a boatload of children but ...we're the only ship in the Quadrant. Spock, these cadets of yours, how good are they? How will they respond under real pressure?

and:

SCOTT: He stayed at his post ...when the trainees ran.

and:

MCCOY: Lieutenant, you are looking at the only Starfleet cadet who ever beat the no-win scenario.

Star Trek III: The Search For Spock

...Most of our trainee crew has been reassigned...

and:

SCOTT: As promised, she's all yours, sir. All systems automated and ready. A chimpanzee and two trainees could run her.

Star Trek IV: The Voyage Home:

KIRK: They're still using money. We've got to find some. Spock! The rest of you stay here. ...The rest of you break up. You look like a cadet review.

Star Trek V: The Final Frontier:

KIRK: General Korrd's military strategies were required learning when I was a cadet at the Academy. When they put me out to pasture, I hope I fare better than Korrd.

They seem to use both midshipman and cadet when talking about Starfleet Academy students, and the only time what seems like an official rank is given it is Peter Preston's Midshipman First Class. Kirk describes himself as being a cadet, not a midshipman, on a voyage to Axanar.

Answer 3

Something else to consider:

Although I don't recall off the top of my head if favoritism or nepotism has been featured through out the other Star Trek's, and that's not say that Tilly isn't brilliant in her own right, it has been more recently revealed through a bit of a plot tease in Tilly-centric Short Trek episode, Runaway, and more so in the synopsis from a new Star Trek: Discovery Tilly-centric book, The Way to the Stars (coming out in January) that Tilly's parents are Federation Luminaries whom have been pushing Tilly hard at least since she was 16 years old! Perhaps they had some kind of clout?

Despite being an inexperienced Starfleet cadet, Sylvia Tilly became essential to the U.S.S. Discovery finding its way back home from the Mirror Universe. But how did she find that courage? From where did she get that steel? Who nurtured that spark of brilliance? The Way to the Stars recounts for fans everywhere the untold story of Tilly’s past.

It’s not easy being sixteen, especially when everyone expects great things from Tilly. It’s even harder when her mother and father are Federation luminaries, not to mention pressing her to attend one of the best schools that the Federation has to offer. Tilly wants to achieve great things—even though she hasn’t quite worked out how to do that or what it is she wants to do. But this year, everything will change for Tilly, as she about to embark upon the adventure of a lifetime—an adventure that will take her ever closer to the stars….

However, that's not to say that she may not also have been "fast-tracked" through the Academy as user Michael Scott Shappe also stated in his answer, which seems to be vaguely confirmed by Star Trek's Memory Alpha Sylvia Tilly Wiki page,

She rated herself as the best theoretical engineer at Starfleet Academy, and was fast-tracked in order to serve aboard the Discovery.

It's unclear if this was due specifically to Lorca alone or as mentioned, in combination with the political influence of her parents, or if Tilly came to choose Discovery by her own experiences, but it is true given the reveal that Lorca

of the first season is the Mirror Lorca and he would be privy to knowing the the achievements of her Mirror Universe counterpart, that he would likely seek that brilliance in the prime universe, much like he sought out Prime Michael Burnham.