Speed defined the Abdiel class and served as its primary protection. The ships were neither armed nor intended to fight an enemy force at close range. They were expected to lay mines independently far from the main fleet, then disappear. By the time an opponent identified the field, the minelayer should already be elsewhere, and a later sighting should be stale before an interception could be organized. The machinery, light armament, endurance penalty, and service careers all follow this design logic.
Chapter · 42:14-42:48
Speed as the Abdiel class's protection
The closing argument is simple: speed was the class's armour, allowing independent minelaying far from the main fleet.