sentences:  Two versions of the mine were produced - a fully waterproofed version designated "To.Mi.A4531" and the normal "To.Mi.4531".The Topfmine B (To.Mi.B4531) was broadly similar to the "A" version, the principal difference being a smooth case without a raised pressure plate.This version instead had an internal shear groove to prevent water from working its way into the mine and possibly deactivating it.