The offensive was finally launched on the 31st July 1917. The weather, which for a fortnight previously had been fine and dry and had seemed to predict success, broke on the day of the battle, and a merciless rain which changed the whole area of operations to a sea of mud fell without cessation for several days. The Corps in line on the 31st July were from left to right the XIV (Cavan), the XVIII (Maxse), the XIX (Watts), the II (Jacob) and the X (Morland). On the whole the day was one of marked success, the deepest advance being made in the northern sector of the attack. From Westhoek to St Julien the second German line was carried, while north of the latter village the assaulting troops passed the second line and gained the line of the Steenbeek as far as the junction with the French, whose attack had also met with complete success. South of Westhoek the enemy's resistance had been more stubborn, and his positions in Inverness Copse and Glencorse Wood which were strongly held by machine-gun posts proved an impassable obstacle. In this region, however, the German first line was carried, and our troops managed to maintain themselves far enough forward on the Westhoek Ridge to deny the enemy observation over the Ypres plain; the position gained running almost due south from Westhoek east of the line Clapham Junction--Stirling Castle--Bodmin Copse, and thence to Shrewsbury Forest, south of which the German second line was occupied as far as the Ypres-Comines Canal. South of the Canal also the Second Army achieved considerable success. The rain, which began to fall in the afternoon, had a most disastrous effect on the British plan of attack. Movement over the shell-torn ground, which was transformed into a series of bogs, rapidly became impossible apart from a few well-defined tracks, and these naturally became marks for the enemy's guns. The labour of moving forward guns, relieving troops and completing the forward dumps and other preparations for the next bound was increased tenfold. The inevitable delay which ensued was of the greatest service to the enemy, who thereby gained a valuable respite in which he was able to bring up reinforcements. The fighting of the next few days was, therefore, local in character and consisted in clearing up the situation and improving the British positions at various points in the line, in the course of which operations the capture of Westhoek was completed. Numerous counter-attacks by the enemy were successfully resisted, and the line gained on the 31st July was substantially held. * * * * *