Brummer and Bremse combined the mine capacity, speed, and range needed for unusually effective surface raiding. German minelaying submarines had already shown how damaging the mission could be, while a fast cruiser could deliver mines on a much larger scale. A quick sortie could place a dense field near British waters and leave before the defender knew where to search. Britain would then have to patrol and sweep a much wider area than Germany had used to create the threat.
Chapter · 4:04-6:52
Why fast minelayers mattered
The Brummer class illustrates how a fast minelaying cruiser could threaten British waters with far more striking power than a small minelaying submarine.