The echelon below the number indicates the platoon. An upward facing echelon is 1st Platoon, a forward facing echelon is 2nd Platoon and a downward facing echelon is 3rd Platoon. The vehicle number (1-4) is indicated by the two black stripes on the bore evacuator. The headquarters vehicles, A66 & A65, would not have echelons only the 51 markings. I don’t believe that either HQ tanks had the barrel rings.