September, Express joined her sister at Immingham on the North Sea on 8 September, operating under the direct control of the Commander-in-chief, Home Fleet, Admiral Sir Charles Forbes. The two destroyers made their first minelaying sortie in the Heligoland Bight on the night of 9/10 September. and did it again a week later without being detected. They then reverted to ordinary duties for the next several months, before beginning to lay defensive minefields off the English coast in November. On 12 December, the Admiralty formed the 20th Destroyer Flotilla with Express as the flotilla leader; the other ships assigned were Esk and the newly converted destroyers, and . The four destroyers laid 240 mines off the mouth of the Ems on the night of 17–18 December and the two sisters then began a refit at Portsmouth. Express and Esk began to lay more defensive minefields in February 1940, often with the large auxiliary minelayers and . On the night of 2/3 March, the sisters were joined by the newly converted destroyers and in laying mines near Horns Reef, in the Heligoland Bight, that sank the in March, and later the submarines , , and . After resuming defensive minelaying later that month, Express was damaged in a collision with the fishing trawler Manx Admiral off Kinnaird Head on 23 March and was under repair until 24 April. On the night of 9/10 May, Express, Esk and Intrepid laid another minefield in the Heligoland Bight and were diverted on their return voyage to escort Princess Victoria as she mined Dutch waters off Egmond the following night after the Germans invaded the Netherlands on 10 May. This began an intensive series of minelaying sorties in Dutch waters during the rest of the month that saw three German minesweepers sunk on 26 July. The minelaying, however, was interrupted at the end of the month by the need to evacuate the British Expeditionary Force from Dunkirk. On 29 May, Express towed the disabled destroyer clear of a wreck in Dunkirk harbour and transferred many of her evacuees aboard before she could repair her engines later that day. The following day, Rear-Admiral Frederic Wake-Walker, commanding the ships involved in the evacuation, briefly hoisted his flag aboard her. She was lightly damaged by bomb splinters on 31 May, but continued to ferry soldiers back to England. The ship and the destroyer were the last ships to