Submarine ambushes create an operational-security trap

Would submarines let Germany make British intervention in the Channel too costly?

The submarines would need to deploy early to be useful, but that movement could reveal the plan or trigger an incident before the landing began.

A proposed submarine ambush creates an operational-timing problem. Both sides would want submarines in position, but the German boats were slow enough that they would probably need to deploy in advance. That movement could compromise surprise or cause an incident, making submarines useful but risky rather than decisive. Tactical opportunity runs directly into intelligence warning, diplomatic restraint, and mobilization timing.