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Traverse to former Shifting House, Lower Upnor Ordnance Depot

A Grade II Listed Building in Frindsbury Extra, Medway

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Latitude: 51.4075 / 51°24'26"N

Longitude: 0.5272 / 0°31'38"E

OS Eastings: 575866

OS Northings: 170633

OS Grid: TQ758706

Mapcode National: GBR PPH.N3Z

Mapcode Global: VHJLN.3W2F

Entry Name: Traverse to former Shifting House, Lower Upnor Ordnance Depot

Listing Date: 7 September 2011

Grade: II

Source: Historic England

Source ID: 1402942

Location: Frindsbury Extra, Medway, ME2

County: Medway

Civil Parish: Frindsbury Extra

Traditional County: Kent

Lieutenancy Area (Ceremonial County): Kent

Church of England Parish: Frindsbury All Saints

Church of England Diocese: Rochester

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Traverse to former Shifting House, Lower Upnor Ordnance Depot, 1811.


Traverse to former Shifting House, Lower Upnor Ordnance Depot, 1811. A traverse is a protective earthwork. sometimes revetted (as here), which is placed to ensure that any accidental explosion in the structure it is protecting (here the shifting house), is contained.

MATERIALS: Earth traverse with retaining walls of yellow stock brick in Flemish bond.

PLAN: A broadly triangular traverse with long walls to the west and east and a short return to the north.

The Lower Upnor Ordnance Depot comprises a site oriented north-south adjacent to the west bank of the River Medway and immediately north of Upnor Castle (built 1559-67, SM 27007, Grade I).

The traverse to the now demolished Shifting House is located in the extreme south of the site to the immediate north of Upnor Castle and to the south of the Grade II* listed B magazine. The traverse wall runs up-slope to the south, with a rising coping, enclosing and retaining an almost triangular earth embankment. The traverse wall therefore retains the north, west and east sides of the broadly triangular traverse. The traverse was very overgrown at the time of inspection. However, the revetment wall was part-visible on all sides confirming the presence of brick on all sides, and the visible brickwork is homogenous. At the north-west corner is a square pier where the traverse wall returns.


Upnor Castle was designed by Sir Richard Lee, a military engineer, and built between 1559 and 1567. Other than the Tower of London it has the longest association with the storage of explosives of any site nationally. Although built as a fort on the strategic River Medway, its defensive function declined after the Dutch Medway raid which led to a re-evaluation of the country's defences. From 1668 it was converted into a magazine and store, the castle having to be adapted in order to fulfil this role. It continued to function as an ordnance store 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 CRE, Colonel D'Arcy. The site chosen was a former ballast wharf and the landscape had already been part quarried creating natural traverses ideal for an ordnance storage function. 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 (details of which can be found in Barker 1998). In 1891 the Army'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. The Lower Upnor 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 site remains (March 2011) with the MoD but is surplus to requirements and will be disposed of in the near future.

The Upnor Depot is part of a Medway complex of ordnance storage. Beginning with Upnor Castle, ordnance facilities expanded on the Lower Upnor site and to Chattenden as described above. The final component of the group was the Lodge Hill site, adjacent to Chattenden, begun in 1899-90. The Medway Ordnance stores served Chatham Dockyard and the Navy in the same way that Priddy's Hard, Tipner Point, Bedenham, Frater and Marchwood served Portsmouth (Hampshire) and Bull Point served Devonport (Plymouth, Devon).

The Shifting House at Upnor was built in 1811. A shifting house was a building where gunpowder was inspected following unloading from ships onto the wharf. Both the barrel and the powder were examined to assess their efficacy and stability before being moved to the main magazine for storage. The Shifting House was part of the primary C19 phase of development at Upnor. Initially intended to inspect dubious powder from the two floating magazines Marquis of Huntley and Delft, it then rapidly became the receiving and inspection point for powder destined for storage in the adjacent A magazine to the north (constructed in 1808-10). Upnor was the first site nationally where a magazine was built with an associated traversed shifting house. Both the Shifting House and A magazine were demolished in 1964 when the depot passed to the Royal Engineers although their footings survive as archaeological deposits.

The Shifting House was a light timber structure on brick foundations deliberately designed so that in the event of explosion the building would essentially lift off. It was therefore necessary to protect it from the rest of the depot by traverses and blast walls. These were built on three sides (to the south, west and north). The form of the traverses and blast walls for the Shifting House are shown on a site plan of 1812 (WO 44/140 reproduced in Evans 2000, 3). The Shifting House was built in a position almost equidistant from the castle and A magazine and the gaps between were filled with angular traverses. The angular form of the surviving south and west traverse is clearly shown. In 1857, the construction of the very large (now demolished) No 1 Shell Store in the gap between the Shifting House and the A Magazine necessitated the demolition of some of the northern traverse closest to the river.

Reasons for Listing

The traverse to the former Shifting House of 1811 at the Lower Upnor Ordnance Depot is listed at Grade II for the following principal reasons:
* Form: a substantial traverse with brick retaining walls whose form reflects its function, built as it was to protect the Ordnance Depot and Upnor Castle from any explosions caused by the inspection of gunpowder and barrels in the associated (now demolished) shifting house;
* Date: built in 1811, the traverse is part of the primary phase of the development of the Lower Upnor Ordnance Depot which was to serve Chatham Dockyard and the fleet into the C20;
* Primacy: the Lower Upnor Ordnance Depot was the first site nationally where a purpose-built traversed shifting house was built, later adopted by other ordnance sites. While the Shifting House no longer survives above ground; the traverse remains a physical manifestation of the innovations in the safe handling of powder.
* Group value: with other listed ordnance structures on the Lower Upnor Ordnance depot which collectively tell the story of the technological development in munitions and the role of Upnor as supplier to Chatham's fleet for over 200 years.

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