Overview: By the numbers the Battle of Loos was a defeat for the British Army but they learned valuable lessons for the future on the Western Front. The creeping artillery barrage is used for the first time successfully and it is apparent that assault tactics have to be rethought completely. On the Balkans, Bulgaria officially declares war on Serbia and joins the Central Powers Germany, Austria-Hungary and the Ottoman Empire. On the same day they invade Serbia which is now in real trouble.