In an atmospheric environment, Spare Engines provide lift for massive Warships. In a vacuum, these engines can be used to provide small course corrections. While a Warship won't flounder without them, their absence will reduce agility. Spare Engines by themselves are defenseless, but the other defenses of a Warship tends to provide enough protection...except against dogged R-craft pilots, in a fighter with whose Wave Cannon is stronger than all the Warship defenses combined.
Controls the vertical direction of the Warship.