 On 4 September 1939, together with sister ships "M75" and "M84" assisted the minelayer in laying a minefield at the southern end of the Øresund.The 7th Minesweeping Flotilla, including "M85" was deployed to Polish waters on 5 September.On 1 October 1939, shortly after the garrison of the Hel Peninsula had agreed to surrender, ending the Battle of Hel, "M85" struck a mine north east of Jastarnia, which had been laid by the Polish submarine .