The 378th Cruiser Squadron consisted of three Constitution-class heavy cruisers that were assembled by Starfleet Command in 2282 and 2283, during a period when the Organians seemed to have lost interest in Federation-Klingon affairs.
USS Excalibur, USS El Dorado, and USS Lexington were assigned to the squadron during the Klingon Empire's Taal Tan Offensive. On 7 July 2283, the 378th engaged a battle fleet of nine Klingon vessels. Excalibur and El Dorado sustained damages in the attack, but the Klingons were beaten back across the border. (The Taal Tan Offensive)