Reinhardt toward the ports — the Arras threat

After his delayed start at Monthermé, Hans-Georg Reinhardt had pursued his advance westward. On 21 May, his XLI. Armeekorps reached Saint-Omer, in the Pas-de-Calais, some 50 miles north of Abbeville where Guderian had just touched the Channel. His mission was now plain: race for Boulogne, Calais and Dunkirk, the three ports by which the British Expeditionary Force might evacuate. Kempf's 6. Panzer-Division was advancing on Calais by way of Aire-sur-la-Lys.

Since crossing the border, his tanks had already covered hundreds of miles in eleven days. The Panzers' rush to the sea had driven the Allied armies of the north into a vast pocket, now threatened with complete encirclement.

But at 14:00 on this 21 May, an unforeseen counter-attack broke out at Arras: Major-General Franklyn's British Frankforce launched some 74 Matilda tanks against the flank of Rommel's 7. Panzer. It was the first real German setback of the campaign; Rommel himself would describe in his notes a brief moment of dismay. The threat was serious — the Matildas resisted the 37 mm guns — and it worried the German command about the solidity of the northern flank. Reinhardt had to decide on the pace to set.