I am currently doing some research into some members of the 254th Indian Tank Brigade and have hit a brick wall with some abbreviations. Does anyone know what the following are? The first is a unit that a Corporal served with. 400 I.S.S. Royal Tank Regiment. The second is a rank of a soldier in a Tank Transporter Coy. M.S.S. I am thinking along the lines of Mechanic Staff Sergeant. Your help would be appreciated.