Nine days of minelaying would advertise the invasion

The German plan allowed nine days to lay minefields protecting the ends of the invasion corridor. These involved thousands of mines, with one field estimated at roughly 3,000. Mine barriers made sense for a navy weakened by losses in Norway. Their construction would nevertheless be difficult to conceal from the Royal Navy. The objection is that the scheme depends on British forces neither recognizing the preparations nor sending minesweepers to interfere during that long interval.