Why a minelayer needed extreme speed and 4-inch guns

Why were the Abdiel-class minelayers so fast, and what could threaten them?

Speed let them lay mines in dangerous waters and escape; aircraft were the main pursuers their 4-inch battery needed to deter.

The operating concept sends a fast minelayer into waters where a new minefield can obstruct enemy movement. It then withdraws before heavier surface ships can catch it. Aircraft remain a threat, which explains the emphasis on 4-inch guns for air defence. When small torpedo boats are suggested as pursuers, the reply points to those guns and the difficulty of approaching a fast ship's bow wave.