The Copperhead was a one off command cruiser, created from a Class I primary hull, coupled to a specially converted shipping container coupled to warp drives.
The design was conceived to meet an urgent need for a command ship capable of controlling operations across a broad battlefield. The single Copperhead, with a strategic operations crew of almost 400 could easily coordinate hundreds of ships across the entire battle space.
The end of the war in 2256 meant the Copperhead was left with a mission, as the peacetime Starfleet could ill afford the level of resources required. The sensor and communications equipment was still of use, so the ship was redeployed to fill a role providing intelligence around the Romulan Neutral zone.