[9] Olav Tryggvason boarded the City of Flint with one officer and thirty armed sailors, who returned control of the ship to the American captain, Joseph H. Gainard, on 6 November.

They had been challenged at the very entrance to Oslo Fjord, where the Norwegian mine layer, Olav Trygverson, sank a German torpedo boat and damaged the light cruiser Emden"[14] The minelayer's commander, kommandørkaptein T. Briseid, had received warning of the intruding foreign naval forces and at 0215hrs anchored his ship to a buoy in the inner harbour to cover the harbour entrance with her guns.

Despite the best efforts of the Norwegian ships, the R 27 managed to get to the cover of a peninsula and land her force of forty-five infantry in the harbour, having suffered several hits in the process.

At the same time as the German minesweepers made their charge into the harbour, the Albatros tried to engage the Norwegian ships, but suffered hits from Olav Tryggvason and was forced to take cover behind some nearby islands.

During the battle Olav Tryggvason fired almost sixty 12 cm shells,[19] suffered at least thirty-five hits from the 20 mm guns aboard the räumboots and had two sailors wounded.

[21] Brummer spent her first year as a Kriegsmarine minelayer on the coasts of the Netherlands and Belgium as part of the naval contingent for the planned invasion of England.

[5] Brummer arrived at Utö in Finland together with the German minelayers Tannenberg and Hansestadt Danzig on 14 June 1941, and was concealed in the Nagu area in preparation for the outbreak of war eight days later.

[23] The mine barrage, codenamed Apolda,[24] channelled shipping in the Gulf either to the north, within reach of Finnish coastal artillery, or to the south, where German guns were in range.

[23] For most of the mining operation, which was initiated in the early hours of the day, the minelaying group worked unchallenged even though the ships were spotted by Soviet naval forces.

On 1 July the Baltic Fleet M class submarine M-81 struck one of the mines laid by Brummer[25] and sank off the island of Vormsi in Estonia.

In the end, the operation failed to attract Soviet interest and saw the loss of the Finnish coastal defence ship Ilmarinen to naval mines.

[5] The end of Brummer came on 3 April 1945, when she was wrecked by RAF bombers while dry docked for repairs at the Deutsche Werke shipyard in the Baltic port of Kiel.