Battle of Loos — First British Use of Poison Gas

Britain used chlorine gas for the first time at the Battle of Loos, releasing it from cylinders along a six-mile front. The wind shifted and blew gas back onto British lines in some sectors. Despite initial gains, the battle failed: reserves were committed too late, and German counterattacks retook most captured ground. Commander-in-Chief Sir John French was blamed for withholding reserves and replaced by Haig in December 1915.