when world war ii began, "z16 friedrich eckoldt" was initially deployed in the baltic to operate against the polish navy and to enforce a blockade of poland, but she was soon transferred to the german bight where she joined her sisters in laying defensive minefields. she also patrolled the skagerrak to inspect neutral shipping for contraband goods in october. on the night of 17/18 october, rear admiral ("konteradmiral") günther lütjens, aboard his flagship "z21 wilhelm heidkamp", led "eckoldt", "z19 hermann künne", "z17 diether von roeder", "z18 hans lüdemann", and "z20 karl galster" as they laid a minefield off the mouth of the river humber. the british were unaware of the minefield's existence and lost seven ships totaling . on the night of 18/19 november, "eckoldt" and "hans lody", led by commander ("fregattenkapitän") erich bey in his flagship "erich steinbrinck", laid another minefield off the humber estuary that claimed another seven ships of 38,710 grt, including the polish ocean liner of 14,294 grt.