USS Excalibur Class Advanced Cruiser (Phase-I Constitution Upgrade)

After the M-5 Computer crippled the USS Excalibur in 2268 during a war-games excercise, the USS Excalibur was towed back to Starbase One for repair. During this repair the lessons learned from the M-5 incident, the contact with the Klingons, Romulans, Tholians, Gorn, and other alien races caused Starfleet to begin the upgrade of the Constitution class design. The first retrofit was the Phase-I Excalibur class refit/upgrade commenced in 2268 and completed in 2269. The Phase-I ship had improved engines (smaller and lighter than the Constitution class, but with greater output), improved shields, and the new Mark-V "Blooming" Phasers that fired a pulse of antimatter surrounded by a phaser-beam that detonated on impact with matter causing a "bloom" of destructive energy. These phasers were a vast improvement over the Mark-IV used on the Constitution class and other ships of the era.