Class X is a starship classification term used to describe a type of starship in relation to other starship types in similar fleets.

In the 24th century, the Decker-class starship was considered to be a class X transwarp destroyer by the Federation Starfleet. (FASA RPG module: Star Trek: The Next Generation Officer's Manual)

Starship classification
By type	argosy • assault ship • attack cruiser • attack fighter • battle cruiser • battleship • bird-of-prey • bomber • cargo transport • carrier • colony ship • combat support tender • construction ship • corsair • corvette • courier • cruiser • cutter • destroyer • dreadnought • escort • explorer • fast attack ship • fast cruiser • flagship • freighter • frigate • fuel transport • gunboat • heavy cruiser • heavy escort • hospital ship • liaison cutter • light cruiser • light frigate • medical frigate • medium cruiser • mining freighter • missile cruiser • monitor • passenger liner • patrol cruiser • personnel carrier • prison barge • repair tender • research vessel • research cruiser • runabout • scout • sleeper ship • star battleship • star cruiser • strike cruiser • super carrier • support frigate • surveyor • tanker • tender • timeship • transport • troop transport • tug • warbird • warpshuttle
Alphanumeric	I • II • III • IV • V • VI • VII • VIII • IX • X • XI • XII • XIII • XIV • XV • XVI