On July 27, zero day was fixed for the 10th, but on August 6 this was changed to the 8th. All this time, in order to maintain secrecy, no mention of the impending attack was permitted, and the only preparation which could be undertaken was to send one officer of the Tank Corps General Staff to the area of operations to study the ground. On July 30 a conference was held at the 5th Tank Brigade headquarters at Vaux, at which the Fourth Army Commander explained the plan of operations. From this day on preparations were begun, the railway moves being issued the same evening.
As already stated, the original proposal was a limited operation, the centre of the attack being carried out by the Canadian and Australian Corps. The right of the Canadians was to be covered by the French First Army attacking east and south-east of the Luce river. The left of the Australians was to be protected by two divisions of the IIIrd Corps operating towards Bray. On July 29 the scope of the operation was extended as follows:
To disengage the Amiens-Paris railway by occupying the line Hangest—Harbonnières—Mericourt.
To advance to the line Roye—Chaulnes, driving the enemy towards Ham, and so facilitate the advance of the French on the line Noyon-Montdidier.
The force placed at the disposal of the Fourth Army consisted of the following Corps:
(i) The Canadian Corps—4 divisions.
(ii) The Australian Corps—4 divisions.
(iii) The IIIrd Corps—2 divisions.
(iv) General Reserve—3 divisions, to be supplemented by further divisions as soon as possible.
(v) The Cavalry Corps—3 cavalry divisions.
Tank battalions were allotted to the 3 infantry corps as follows:
(i) Canadian Corps, 4th Tank Brigade—1st, 4th, 5th, and 14th Battalions.
(ii) Australian Corps—5th Tank Brigade—2nd, 8th, 13th, and 15th Battalions.
(iii) IIIrd Corps—10th Battalion.
(iv) General Reserve—9th Battalion (still refitting at Cavillon).
(v) Cavalry Corps. 3rd Tank Brigade—3rd and 6th Battalions.
The 3rd and 6th Battalions were equipped with 48 Whippet tanks each; all the other battalions were heavy units equipped with 42 Mark V machines each (36 fighting and 6 training tanks), except the 1st and 15th Battalions, which were each equipped with 36 Mark V One Star machines.