German submarine-borne raids on Britain

What if Germany launched submarine-borne commando raids on the British Isles during the First World War?

The first might gain surprise, but later attempts would probably fail as coastal patrols and a locally raised home-defense force expanded.

Submarines might land a raiding force once before Britain understood the threat. Thereafter, obsolete cruisers and other patrol vessels could monitor the coast and attack a submarine caught unloading troops. Political pressure for home defense might also create a First World War equivalent of the Home Guard, drawing on armed Boer War veterans rather than repeatedly diverting front-line troops from France.