Laying mines in an enemy's supposedly safe channels

The discussion describes laying a British minefield around a German field so that routes believed clear became dangerous. A second example concerns Sunderlands dropping mines into mapped gaps in Baltic minefields. In this account, uncertainty over whether German mines had broken loose diverted minesweepers into checking their own fields. The explanation also mentions mines fused to threaten minesweepers. These examples concern the disruption of known routes and clearance work, rather than a minefield's size alone.