Winston Churchill sends a telegram to President Roosevelt regarding his request for U.S. destroyers. Churchill acknowledges FDR's problems in providing them but states that, "If they were here in six weeks they would play an invaluable part."

NETHERLANDS: Arthur Seyss-Inquart, the former Austrian chancellor, is appointed Reich Commissioner for the Netherlands.

FRANCE: At 2 am Hoth’s Corps in the north was set in motion again, with Rommel at its head, and pushed up to the heights of Arras, which seemed very important to the German High Command. "We will only have won", wrote Halder, "when we have taken Arras high plateau"; and he expected "a decisive battle lasting several days" in this area.

When he arrived south-east of Arras, Rommel took up defensive positions. He made ready to by-pass the town on the following day on the south, and then to proceed to the famous heights north of Arras, where so much blood was shed in 1915.

In the south Guderian’s Panzers set off from the line of Cambrai-Peronne before dawn. A about 9am, the 1st Panzers, on the left, easily captured Amiens, in the presence of Guderian, who had particularly wished to witness this "historic event". Then it established a bridgehead about 4 miles deep on the south bank of the Somme.

On the right, the 2 Panzers made a thrust from Albert towards Abbeville, through Doullens, Bernaville, and Beaumetz. At 7pm it seized Abbeville without much difficulty. From there it sent out one tank battalion, which reached the sea at Noyelles at dusk.

With understandable joy, the Panzer crews, who had crossed the Meuse scarcely a week before, filled their lungs with the sea air and their eyes with the sight of the sea.

When the Fuhrer got this news, "he was beside himself with joy", declared Jodl, "and he already foresaw victory and peace". The French army was now definitely cut in two.

"In the evening of this memorable day", wrote Guderian, "we did not know in which direction we were to continue to advance. General von Kleist himself had no orders. May 21 was spent waiting for orders. I employed the time visiting Abbeville and making an inspecting of the Somme bridgehead."

It was towards the end of the day that orders arrived from OKH for a swing northwards in order to seize the Channel ports and the Pas de Calais. Guderian then gave orders to the 1st Panzers, in the right, to start the next day straight for Calais, through Samer and Desvres; he told the 2nd Panzers, on the left, to head for Boulogne by going along the coast. On Guderian’s right, Reinhardt’s Corps was to go between Doullens and Arras and advance to Saint-Omer, but at the pivoting point, on the right, we shall see that Hoth’s Corps was held up in the Arras area.

Berlin Diary by William Shirer:

We came to a terrific hole in the road ... The German officer explained that the French blew this one up. "French dynamite experts," he said. "At places they have done a beautiful job ... We lost little time," he added, "even though you have to admit the French did a good job of it here." His admiration for the French dynamiters was terrific.

Paris: Reynaud sacks Gamelin and replaces him with General Maxime Weygand. Until now Weygand has been in virtual exile in Syria, now his appointment as Supreme Commander is hailed in the press; but he is a staff officer who has never commanded armies in battle. He has disregarded plans already made for the Allied armies in north and south to attack and cut off the exposed German armoured columns, still unprotected by infantry. He spent his first day making ceremonial visits to the French president and cabinet ministers. Then he said he would visit the front, as his hero Foch had always done. He set off by air for Ypres to talk to French, British and Belgian commanders. During the meeting King Leopold decided that Weygand was completely ignorant of the plight of the Allied armies.

GERMANY: U-403 laid down.

NORWEGIAN CAMPAIGN: (Mark Horan) Word having arrived that the weather was improving over Narvik, at 0330 HMS Ark Royal, in position 70.24N, 16.10E, dispatched nine Swordfish of 810 and 820 Squadrons (armed with either 4x20 lb Cooper, 4x25 lb Incendiary, and either 2x500 lb or 4x250 lb bombs). This mission exhausted the last 250 lb GP bombs on the ship. At the same time a fighter patrol left for Narvik. At 0400, a second fighter patrol departed with orders to cover the Swordfish in their attack on the Hundallen and Sildvik. Unfortunately, the weather deteriorated drastically and the entire force had to abandon their mission and return to the ship.

At 0600 a further fighter patrol was dispatched. While it managed to get to the Narvik area, the weather was atrocious and the trio was lucky to find their way back to the ship. Further flying was suspended. However, at 2101 Flag Officer Narvik informed the Vice-Admiral commanding that Bardufoss landing ground now being operational, HMS Furious should dispatch the Gladiators of 263 Squadron to shore on the 21st.