From the perspective of the Chiefs of Staff, they were concerned about the German presence in Crete, and the prospect that the Germans could supply their forces in Cyrenaica from western Greece. The Chiefs of Staff wanted to have airfields forward between Derna and Sollum in Cyrenaica to interfere with such a supply line. Therefore, General Wavell needed to attack to take that area. Never mind the fact that he had only just received his 238 tanks which had made a long sea voyage and they would need to be prepared. Also, if it is true that the shipment included some brand new Crusader I's, they had not yet had the mechanical bugs worked out of them, and they would be a liability. Others needed a mechanical overhaul, which seems odd for tanks that were supposed to be used immediately. Oddly enough, the 7th Armoured Division had been dissolved, and needed to be totally reconstituted. Some of its constituent units had operated independently, or under the command of other units.
The plan for Battleaxe was to defeat the Germans in the frontier area and then advance to the vicinity of Tobruk and defeat the Germans there. From there, the British would advance to Derna and Mechili. This is based on the account in Vol.II of the Official History.