Outside the German mine-fields, and in any inshore areas which were unmined, German patrol craft would probably be stationed.
The point they chose was the nearest practicable bay that was unmined.
"pit or tunnel in the earth for obtaining metals and minerals," c.1300, from Old French mine "vein, lode; tunnel, shaft; mineral ore; mine" (for coal, tin, etc,), of uncertain origin, probably from a Celtic source (cf. Welsh mwyn, Irish mein "ore, mine"), from Old Celtic *meini-. Italy and Greece were relatively poor in minerals, thus they did not contribute a word for this to English, but there was extensive mining from an early date in Celtic lands (Cornwall, etc.). From c.1400 as "a tunnel under fortifications to overthrow them."
explosive device, by 1850, from mine (v.2).
to dig, c.1300, "to tunnel under fortifications to overthrow them," from mine (n.1) or from Old French miner "to dig, mine; exterminate." From mid-14c. as "to dig in the earth" (for treasure, etc.). Figurative use from mid-14c. Related: Mined; mining.
"lay explosives," 1620s, in reference to old tactic of tunneling under enemy fortifications to blow them up; a specialized sense of mine (v.1) via a sense of "dig under foundations to undermine them" (late 14c.), and miner in this sense is attested from late 13c. Related: Mined; mining.
The process of mining is described in Job 28:1-11. Moses speaks of the mineral wealth of Palestine (Deut. 8:9). Job 28:4 is rightly thus rendered in the Revised Version, "He breaketh open a shaft away from where men sojourn; they are forgotten of the foot [that passeth by]; they hang afar from men, they swing to and fro." These words illustrate ancient mining operations.