Research for tank casualties in Normandy from 6 June to 10 July 1944 conducted by the British No. 2 Operations research concluded, that from a sample of 40 Sherman tanks, 33 tanks burned (82 percent) and 7 tanks remained unburned following an average of 1.89 penetrations. In comparison, from a sample of 5 Panzer IVs, 4 tanks burned (80 percent) and 1 tank remained unburned, following an average of 1.5 penetrations. The Panther tank burned 14 times (63 percent) from a sample of 22 tanks and following 3.24 penetrations, while the Tiger burned 4 times (80 percent) out of a sample of 5 tanks following 3.25 penetrations. John Buckley, using a case study of the British 8th Armoured Brigade (United Kingdom) and 29th Armoured Brigade (United Kingdom), found that of their 166 Shermans knocked out in combat during the Normandy campaign, 94 (56.6 percent) burned out. Buckley also notes that an American survey carried out concluded that 65% of tanks burned out after being penetrated. United States Army research proved that the major reason for this was the stowage of main gun ammunition in the vulnerable sponsons above the tracks. A U.S. Army study in 1945 concluded that only 10-15 percent of wet stowage Shermans burned when penetrated, compared to 60-80 percent of the older dry-stowage Shermans.
Question: How many days did the British No. 2 Operations research for tank casualties?
Answer: 4