Starfleet Officer Accession Ranks are those Starfleet ranks held by persons in the universe of Star Trek who wish to become commissioned officers of the Starfleet.

The process of becoming a Starfleet Officer is little explored, with most references being made to Starfleet Academy, a four year training university similar to the United States Naval Academy. Since Star trek’s beginnings, “the Academy” has evolved from simply being mentioned in dialogue, to eventually being seen, and finally fully described as a military academy.

Apart from Starfleet Academy, there has been very little reference to extra-commissioning programs with the exception of brief segments in the Star Trek Expanded Universe. A significant extra-commissioning program, however, was explored with the character of Wesley Crusher who entered into an “Acting Ensign” program where he trained to become an officer before attending Starfleet Academy.

Cadet is the most well known Starfleet rank held by Starfleet student officers in the fictional Star Trek universe. In the Original Series era, Academy students are also sometimes referred to as "midshipmen" (TOS: "Court Martial", Star Trek II: The Wrath of Khan).

The rank is established in Star Trek through dialogue referring to Starfleet Academy. Only two Starfleet cadets appear in The Original Series: a recreation of Cadet Finnegan (TOS: "Shore Leave") and an unnamed cadet in a bar (TOS: "Wolf in the Fold"). In both cases, the cadets wear a silver-gray tunic with a starburst chest emblem.

Starfleet cadets do not appear again until Star Trek II, in which they are referred to as both cadets and midshipmen. In the film, cadets wear red undertunics and a red shoulder tab. Some of these midshipmen, including Saavik, also wear commissioned officer insignia. Star Trek II marks the last time Academy students are referred to as "midshipmen."

In Star Trek: The Next Generation, the rank of cadet is firmly established as the title held by Starfleet Academy students. Cadets in TNG wear a black jumpsuit with red shoulders and a Starfleet commbadge. Cadets' year at the Academy is indicated by a collar device (TNG: "The First Duty").

One cadet imposter wears a uniform with yellow shoulders and no insignia (TNG: "Allegiance"). Wesley Crusher loses his field commission as an ensign aboard the USS Enterprise upon his matriculation to Starfleet Academy, becoming a cadet (TNG: "The First Duty").

Cadet uniforms in Star Trek: Deep Space Nine are mainly gray rather than black but retain the red shoulders. They do not wear a collar insignia. Nog becomes the first Ferengi in Starfleet upon his entrance into Starfleet Academy (DS9: "Homefront"). His cadet field training includes a tour aboard Deep Space Nine (DS9: "The Ascent") and he later receives a battlefield commission to ensign (DS9: "Favor the Bold").

The non-canon Star Trek: The Next Generation Officer's Manual roleplaying book says that the rank of midshipman is bestowed on Starfleet cadets who have graduated from the Academy and are posted to an assignment on "probationary status" prior to commissioning as ensigns.

The non-canon novel Doctor's Orders refers to the cadet rank of "officer candidate". Such a rank is held by "direct commission" personnel, such as scientists and doctors, who do not attend Starfleet Academy prior to be commissioned as officers. This mirrors the United States military practice of appointing educated civilians, such as lawyers and doctors, to the rank of officer candidate for a relatively brief training period prior to being commissioned.

The uniform worn by Wesley Crusher, serving as an "acting ensign" in TNG''s second and third seasons, is an oddity in that the uniform is never explained on screen nor does any other character in a subsequent Star Trek episode or series wear a similar uniform. The uniform is a light grey tunic, with a sweater-like shoulder piece, that is worn without any identifying insignia except an all-silver (rather than a silver arrowhead on gold background) communication pin (TNG: "The Child"). The producers said in later years that this uniform was designed along the lines of a "Starfleet West Point" look created to give Wesley a more military appearance, gearing the character away from the child-like character seen in the first season^{[citation needed]}. In the first season, after being named an "acting ensign," Wesley wear a sweater similar to those that he had worn before but with red, yellow, and blue stripes – Starfleet division colors – across the top (TNG: "Lonely Among Us").

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