The British continued their successful minor operations during the succeeding days. On February 20, 1917, New Zealand troops penetrated German lines south of Armentières to a depth of 300 yards, where they wrecked dugouts and trench works. The intense preliminary bombardment which preceded the raid had proved so destructive that the New Zealanders found the German support lines filled with dead. The raid resulted in the capture of forty-four prisoners. In an attack southeast of Ypres the British, advancing on a front of 500 yards, reached the German support line after desperate fighting. They destroyed dugouts and mine shafts and took 114 prisoners, including an officer and a number of machine guns.
The steady pressure of the British on the German positions along the Ancre since the beginning of the month brought results that surpassed Field Marshal Haig's most sanguine expectations. The Germans were forced to abandon their front on the Ancre, escaping to a new line of defenses along the Bapaume ridge. Their retreat covered about three miles and the British were able to occupy a number of German strongholds which they expected to win by hard fighting. Serre, the two Miraumonts, and Pys were occupied without a struggle. The Germans succeeded in saving their guns during the retirement, but were forced to destroy ammunition dumps and military stores. In the night of February 24, 1917, British troops, advancing south of Irles and toward Warlencourt, occupied the famous butte which had been the scene of intense fighting in the previous month.
The foggy, misty weather which prevailed at the time in this region had greatly facilitated the German retreat, as the keen eyes of the British airmen were unable to study their movements. It was surmised that some important operation was under way owing to the reckless expenditure of shells which had been going on for some days. The Germans were shooting up stores of ammunition which they found impossible to take with them in their retreat.
During February 25-26, 1917, the British continued to harass the retiring Germans, pressing forward over the newly yielded ground and forcing back the rear guards of the enemy. In these actions the Germans depended chiefly on their heavy guns mounted on railway trucks, which in case of necessity could be rushed away at the last moment.