The 1935 edition of the War Office publication, Field Service Regulations (FSR), containing the principles by which the army was to act to achieve objectives, was written by Major-General Archibald Wavell, made breakthrough the responsibility of infantry divisions with the support of Army Tank Battalions, equipped with specialised vehicles for infantry-artillery co-operation, the slow and heavy Infantry tanks. Once a breakthrough had been created, a Mobile Division containing a tank brigade with light and cruiser tanks, would advance through the gap and use the speed and range of its tanks to surprise the defender and attack flanks, headquarters and non-combatant units. By 1939, further amendments to FSR added counter-attacks on an enemy armoured breakthrough. (The codification of the difference between Infantry and cruiser tanks and their functions in FSR 1935, accidentally created an obstacle to all-arms co-operation that lasted long into the Second World War.) Defence against tanks could be achieved by troops finding physical obstacles and by controlling their own anti-tank guns. The obstacles could be woods and rivers or minefields as long as they were covered by fire from other weapons. In places lacking convenient terrain features, lines-of-communication troops would also need anti-tank guns and be trained to set up localities suitable for all-round defence