General Wavell had reason to be concerned about the stability of the British position in North Africa. They had learned that the 15th Panzer Division had arrived earlier than expected, by 18 April 1941. The British side was short of tanks, between the attrition from the original offensive to those diverted to the Greek adventure and lost. They only had a mixed unit at Tobruk (the 32nd Army Tank Brigade, formerly the 3rd Armoured Brigade) and a squadron of cruiser tanks at Mersa Matruh. From repairs and refurbishing they might be able to increase the inventory of runners by another 30 or 40 tanks in six weeks.
In London, the decision was made on 21 April to send the Tiger Convoy with a mixed cargo of tanks and Hurricanes. These included 135 Inf. Mk.II Matildas, 82 Crusader Mk.I tanks and 21 light tanks, probably Lt.Mk.VIC, and 53 Hurricanes loaded on five relatively fast transports. General Wavell and his staff, based on this expected reinforcement proceeded with planning for the next offensive codenamed Battleaxe.
This is based on the account in Vol.II of the Official History as well as this previous blog post.