Building Lu001 (Former B Magazine), Upnor Depot

Magazine, built 1856-7, designed by Lieutenant Colonel Savage, the Commanding Royal Engineer at Chatham. The building is constructed in English bond brick with stone-coped gables and a corrugated asbestos roof. It has a rectangular plan and rises to two storeys, with an 8-bay west front facing the Medway. Each bay is topped by a segmental brick drip moulding above segmental brick arches, beneath which are first-floor 2-light casements with glazing bars set in deep reveals and double-leaf plank doors. The rear elevation is similar in treatment.

Internally, each bay is spanned by a catenary arch. This fine magazine building represents the most impressive example of a magazine using the catenary arch system, which had previously been employed by the Royal Engineers in the Drop Redoubt and Napoleonic Tunnels at Dover and at Weedon Depot in Northamptonshire. Catenary arch systems also survive at Tipner, Portsmouth, though the similar 1810 magazine at Upnor was demolished years ago. The building is significant for its gabled facades and Tudor Gothic detailing, which give it a strongly architectural character unusual for a 19th-century magazine, possibly a response to its prominent location on the Medway close to Upnor Castle. The result is a structure of major interest both as an example of structural engineering and as an exceptionally fine demonstration of the Royal Engineers' renowned design ability. It also relates to the World Heritage Site at Chatham Dockyard, which lies across the Medway and which the ordnance yard served.

The site has a long history of explosive storage. Upnor Castle, built between 1559 and 1567 to designs by military engineer Sir Richard Lee, has after the Tower of London a longer association with explosives storage than any other site in Britain. After its defensive importance declined following the Dutch raid of 1667, it was converted in 1668 into a store and magazine, a function which continued until 1913. The castle was adapted with laboratory facilities in the south tower and other spaces serving as cooperage and shifting house. From 1827, buildings in the water bastion were lowered to form a new laboratory building, and the castle magazine was converted into a laboratory storehouse.

Plans to replace Upnor Castle with a modern magazine were drawn up by 1806. In 1808, construction began on a magazine with capacity for 10,000 barrels, its site quarried from a rocky hillside to provide natural traverses. Colonel D'Arcy, the senior Royal Engineer, chose catenary vaults rather than rounded vaults to provide greater internal height; these had already been used in casemates at Dover Castle. Some 3,500 barrels continued to be stored in the castle, though this was eventually phased out. Restoving of powder took place at Faversham instead.

The Crimean War exposed inadequacies in the storage provision. A particular difficulty was that filled shells could not be stored in the same magazine as gunpowder; shells were carried through the Laboratory, where gunpowder was being examined and filled into cartridges, then hoisted 20 feet into an adjacent chamber. In 1856, it was decided to build a new shell store and magazine with capacity for 23,000 barrels. Both were completed in 1857. An additional shell store followed in 1860-1. By 1877, with no space for further expansion on the site, a new inland location was acquired at Chattenden for five bulk store magazines, linked to Upnor by railway and serving as a deposit magazine. The Upnor site continued to expand eastwards along the Medway in the late 19th century, with storage for wet and dry guncotton constructed in 1895-6 (the main explosive used in mines and torpedo warheads) and shell filling facilities in 1906-7. The latter, now demolished with only traverses remaining, was built considerably later than equivalent facilities at Priddy's Hard and Bull Point, this function having previously been carried out at Woolwich.