Landships II

Reading a web page on Namibia one part covering diamod mining operations by the Skeleton coast contains the following reference "Towards the end of the operation in the area , there were boreholes for water and the soil was removed by ex first world war tanks converted into bulldozers" Any one  have any idea what these might have been. The account is iinteresting in that it sugests that in the dry environment  these  ex tanks remain partly covered with drifting sand but otherwise uncorroded by time.