On 21st August, the newly arrived Yeomanry would be introduced to battle gently and were planned to be in reserve at Lala Baba, while the infantry, including 5th Dorsets, were to deliver the main attack on Scimitar Hill. Despite the arrival of additional British artillery, the thirty-minute preliminary bombardment was disappointing.
It had been planned to attack in the late afternoon when the setting sun would have been in the Turks eyes but, sadly, the day was overcast. Not only that but Turks had strengthened their positions. However the 5th Dorsets in a well disciplined charge succeeded in reaching the enemy's first line in fine style. Here after a brief but bloody fight with the bayonet the Turkish trench was taken. However, pressing on across rocky ground to the next enemy line, the Dorsets were cut down by fire from a flanking position that another Brigade had failed to take. They withdrew to the first enemy trench, having suffered very heavy casualties, many of whom lying in the fire swept no-man's-land suffered cruelly for want of help.
By late afternoon it was apparent that the infantry attack had broken down and there was nothing for it but to commit the Yeomanry Regiments to their first battle, but delays meant that it would be a night attack. The QODY, led by Colonel Troyte-Bullock, moved forward across the open plain under artillery fire and as dark settled on the battlefield, attacked. Advancing through the burning bushes and scrub, stepping over dead and dying infantrymen and heading up Scimitar Hill towards enemy positions, briefly illuminated by the flashes of gunfire, the Yeomanry surged on. In a 'forlorn hope' charge, men fell, struck by tracer rounds, but the enemy's front line was captured; yet the main Turkish position further up the hill remained intact. Regrouping, the Yeoman attacked again and despite heavy casualties, they seized a foothold in the Turkish main position. However, weakened by their losses the QODY were unable to hold their gains and were ordered to withdraw to Chocolate Hill.
Having lost virtually all the officers and sixty percent of their soldiers the QODY were temporarily amalgamated with the remains of another yeomanry regiment to make a viable unit to hold a section of the line.