In starship classification, a heavy cruiser is a large multi-purpose starship, similar in some ways to an Explorer.
The term heavy cruiser is sometimes used synonymously with battle cruiser in conversation. For example, in 2285 some Klingons referred to the USS Enterprise as a "battle cruiser". (Star Trek III: The Search for Spock) And Jonathan Archer referred to his own Enterprise as a battle cruiser in 2152. (ENT: "Judgment")
- Archer’s use of the term "battle cruiser" was likely just for effect as he was trying to impress the Klingons.
Types of heavy cruisers
- Surak class
References
The Star Trek: Deep Space Nine Technical Manual for all except for the Ambassador class (TNG: "Conspiracy"), and the Constitution class (Star Trek III: The Search for Spock).
Background
The term "heavy cruiser" has been uttered only once throughout all of Star Trek. In TNG: "Conspiracy" it was spoken in reference to the Ambassador class ship. Most other references to large ships have used the term "battle cruiser". (For example, TOS: "The Trouble with Tribbles, TNG: "The Arsenal of Freedom (applied in the script description to the battle section of the Enterprise-D); The Schizoid Man; ENT: Judgment, DS9: Soldiers of the Empire, Star Trek VI: The Undiscovered Country, and many others). The term heavy cruiser first came into use in the Star Fleet Technical Manual. It was used in the script description of the Klingon K’tinga class ships in Star Trek: The Motion Picture, and was thereafter picked up by the production staff on TNG in their behind-the-scenes technical texts (such as the Deep Space Nine Technical Manual). Remnants of the original usage can be seen in background graphics on the bridge in Star Trek III: The Search for Spock.
The actual usage of "heavy cruiser" in navies was based, not on an independent need to describe a ship as such, but solely as a result of a 1921 treaty (supplemented by a 1930 treaty) that sought to limit the size of warships across the globe. The classification fell out of favor following World War II. (See here for more.)
Other than the Ambassador and the Constitution classes, above classifications of any particular class of ship as a heavy cruiser is non canon, but is considered to come from a Memory Alpha permitted resource.