Complex sentence: The principal advance was made by the 18th Division in the centre and succeeded quickly but German artillery began an SOS barrage at from Stirling Castle to Westhoek, which isolated the foremost infantry beyond Inverness Copse and in Glencorse Wood, as local German reserves began immediate counter-attacks.
Split into simpler sentences: The principal advance was made by the 18th Division in the centre and succeeded quickly but German artillery began an SOS barrage at from Stirling Castle to Westhoek. The German barrage isolated the foremost infantry beyond Inverness Copse and in Glencorse Wood, as local German reserves began immediate counter-attacks.