This naturally goes for both, STO and Star Trek.
TOS: "Tomorrow is Yesterday"
This proves that they are at least a navy in a "combined service".
United Earth Space Probe Agency
TAS: "The Counter-Clock Incident"
Star Trek: The Animated Series
TOS: "Catspaw"
Navy bean
Star Trek: Generations, 19th century naval uniforms.
![Star-Trek-Generations-02.jpg]()
DS9: "Rapture"
DS9: "Behind the Lines"
Navy
In the case of Starfleet, it is a fleet of spaceborne military vessels (spacecraft). A real-life navy includes non-combat duties too, but it's still a military service.
USS Enterprise (CVN-65) was an aircraft carrier and the flagship of Nuclear Task Force One in the United States Navy. It is one of the drawings on the ship wall in Star Trek: The Motion Picture and in Captain Archer's ready room (pictured below):
![292?cb=20061012013249&path-prefix=en]()
Star Trek's USS Enterprise carries shuttlecraft, so it's a carrier too.
Naval officers first attend a naval college or academy, such as the United States Naval Academy. This corresponds to Starfleet Academy in Star Trek.
Therefore, Starfleet is a naval force in space that combines military forces such as navy, marine corps and coast guard. It also means that the Federation is a militaristic society.
This should settle it.
TOS: "Tomorrow is Yesterday"
CHRISTOPHER: Must have taken quite a lot to build a ship like this.
KIRK: There are only twelve like it in the fleet.
CHRISTOPHER: I see. Did the Navy
KIRK: We're a combined service, Captain. Our authority is the United Earth Space Probe Agency.
KIRK: There are only twelve like it in the fleet.
CHRISTOPHER: I see. Did the Navy
KIRK: We're a combined service, Captain. Our authority is the United Earth Space Probe Agency.
This proves that they are at least a navy in a "combined service".
United Earth Space Probe Agency
UESPA (pronounced "you-spah") was [. . .] one of several names given in early episodes for the agency under which the Enterprise and its crew operated before writers finally settled on "Starfleet".
TAS: "The Counter-Clock Incident"
APRIL: I was there in the San Francisco Navy Yards when her unit components were built. [referring to the Enterprise]
Star Trek: The Animated Series
With the release of The Animated Series DVD, the studio appears to have changed its stance, and is leaning towards the animated series being part of established Star Trek canon.
TOS: "Catspaw"
DESALLE: Maybe we can't break it, but I'll bet you credits to navy beans we can put a dent in it.
Navy bean
It is commonly known as the "Navy Bean" due to its use as a staple of United States Navy rations in the 19th century.
Star Trek: Generations, 19th century naval uniforms.

DS9: "Rapture"
WORF: That will not do. Rifkin commands a starship. Protocol requires he be given equal quarters.
ODO: But he's only a captain.
WORF: It is naval tradition.
ODO: But he's only a captain.
WORF: It is naval tradition.
DS9: "Behind the Lines"
DAX: Are you two ever going to be finished?
NOG: Just a few more minutes, Commander.
O'BRIEN: That's Captain. It's an old naval tradition. Whoever's in command of a ship, regardless of rank, is referred to as Captain.
NOG: Just a few more minutes, Commander.
O'BRIEN: That's Captain. It's an old naval tradition. Whoever's in command of a ship, regardless of rank, is referred to as Captain.
Navy
A navy or maritime force is a fleet of waterborne military vessels (watercraft) and its associated naval aviation, both sea-based and land-based. [. . .] recent developments have included space-related operations.
[. . .]
In most nations, the term "naval", as opposed to "navy", is interpreted as encompassing all maritime military forces, e.g., navy, marine / marine corps, and coast guard forces.
[. . .]
In most nations, the term "naval", as opposed to "navy", is interpreted as encompassing all maritime military forces, e.g., navy, marine / marine corps, and coast guard forces.
In the case of Starfleet, it is a fleet of spaceborne military vessels (spacecraft). A real-life navy includes non-combat duties too, but it's still a military service.
USS Enterprise (CVN-65) was an aircraft carrier and the flagship of Nuclear Task Force One in the United States Navy. It is one of the drawings on the ship wall in Star Trek: The Motion Picture and in Captain Archer's ready room (pictured below):

Star Trek's USS Enterprise carries shuttlecraft, so it's a carrier too.
Naval officers first attend a naval college or academy, such as the United States Naval Academy. This corresponds to Starfleet Academy in Star Trek.
Therefore, Starfleet is a naval force in space that combines military forces such as navy, marine corps and coast guard. It also means that the Federation is a militaristic society.
This should settle it.