The ROF type is a bespoke design only found at Royal Ordnance depots and factories. It is a small square pillbox with distinctive long narrow embrasures in each wall. The door is low and usually covered by a porch with a slightly angled roof. The long narrow embrasure serves well as an observation slit but not as well as a firing port, this suggests the main function of this type was as an observation and guard post with a secondary role of defensive position in the event of an attack. At some ROF sites the narrow embrasure is replaced by a more standard rifle embrasure and at Norton Fitzwarren AA positions have been added to the roof. The walls are about 8ft long but the size of this type varies slightly across the country.