Sentry post at Lower Upnor Ordnance Depot, of WW1 date. DESCRIPTION: Reinforced concrete sentry post located on high ground in the south-western part of the site and therefore overlooking the Lower Upnor Ordnance Depot and the River Medway. A concrete polygonal (11-sided) structure approximately 2.5m high with a shallow domed roof. S single, small but heavy concrete hatch-doorway with steel-hinges. Vegetation growth precluded easy access but other examples of this type have observation apertures on alternate sides. The visible aperture above the doorway has a deep reveal and very small observation slit. Walls are approximately 30cm (1 foot) thick. Those of similar sentry posts at Chattenden/Lodge Hill, and presumably therefore here, are built in circa 2 feet (60cm) sections; the roof constructed using a corrugated former. The sentry post would have functioned as a point of refuge under fire rather than being permanently occupied and the narrowness of the apertures indicates that it would have been used for observation rather than small arms firing. The Lower Upnor Ordnance Depot is part of a Medway complex of ordnance and ammunition storage. Its origins are at Upnor Castle, to the immediate south, designed by Sir Richard Lee, a military engineer, and built between 1559 and 1567. Although built as a fort on the strategic River Medway, from 1668 it was converted into a magazine and store and continued to function as such until 1913. By the early C19 it was clear that the castle did not have sufficient capacity to store the Navy's armaments and the construction of a modern magazine to the north of the castle began in 1808 under the supervision of the Commander of the Royal Engineers, Colonel D'Arcy, on a former ballast wharf. The Crimean War in the mid C19 again highlighted the inadequacies of the storage facilities (barrels had to be imported to ensure sufficient powder for the siege of Sebastopol 1854-5) and another large magazine and shell store was built, completed in 1857. The capacity of the site for the erection of bulk store magazines was again reached in 1872 when a decision was taken to purchase land for a Deposit Magazine a few miles away at Chattenden. This would service Upnor with the two sites linked by railway. In 1891 the War Office's responsibility for the supply of armaments to the fleet was taken over by the Admiralty and the Upnor depot therefore passed to Admiralty control becoming a Royal Naval Armaments Depot. The depot continued to expand to the north along the west bank of the River Medway with the addition of wet and dry guncotton storage in the late C19 and shell filling facilities erected in the early C20, a function previously carried out at Woolwich. The Upnor sentry post was built as part of the WW1 enhancement of the defences for the depot. Its date is based on form with WW1 pillboxes and sentry posts typically of this type of concrete construction. Current evidence suggests that this type of circular concrete sentry post is a locally distinctive naval form, with all other known examples confined to the Medway. Six were built at Chattenden and Lodge Hill Ordnance Depots as part of the enhancement of the defences there during the First World War. Another is located at the Medway Maritime Hospital site (the former Royal Naval Hospital near the junction of Windmill Road and Langhill Avenue, Gillingham), and there are two at the Bull Nose, Gillingham Docks. A reinforced concrete sentry post, built to enhance the defences of the Lower Upnor Ordnance Depot during WW1, is listed at Grade II for the following principal reasons: * Early date: relatively few examples are known from the First World War and so this sentry post is a rare survival nationally; * Rarity: an example of a sentry post design which is believed to be unique to Royal Navy sites in the Medway area of north Kent; * Group value: with other listed structures on the Ordnance Depot including B Magazine (1856-7, Grade II*) and the River Wall (early C18, Grade II); also as part of a group of contemporary Medway Naval defensive structures including other sentry posts at Chattenden/Lodge Hill built broadly to the same specification to reinforce the defences of these three connected ordnance depots.