 Complete the following phrase:  By now Arras was becoming a salient in the German lines and increasingly vulnerable. The four Brigades of the 5th and 50th Divisions were becoming hard pressed and on the night of 2324 May received orders to withdraw to the canal line. After fighting on the canal line the 5th and 50th Divisions were withdrawn north to Ypres to fill a threatening gap developing between the Belgian Army and the BEF, after a strong German attack on the Belgians on 25 May. It was late on 27 May when the 50th Division arrived at Ypres to find their positions already being shelled and the Belgian Army being pushed north-eastwards away from them. The gap was covered by the side-stepping 3rd Division the next day. On that day 28 May the Belgians surrendered, opening up a 20-mile gap south from the English Channel, which the Germans aimed to exploit rapidly . The division was now ordered to form a line east of Poperinghe, with the 3rd Division east of them up to Lizerne, this was done by the morning of 29 May, forming the southern edge of the Dunkirk corridor. In contact with the Germans from the start the 50th Division was forced back and by late 30 May was in the eastern end of the Dunkirk perimeter. The division was reinforced by some remts from the 23rd Northumbrian Division on 31 May, which were needed as the Germans continued to attack and shell the 50th Divisions positions. Withdrawn to the beach on 1 June, the 151st Brigade was informed it may be used in a diversionary attack to cover the evacuation and formed two columns, but this became unnecessary. That night the 50th Division was 