The Isle of Sheppey, which is about 9 miles long and 4-1/2 wide, lies on the south side of the Thames estuary and is separated from the north Kent coast by a narrow channel called the Swale.
Sheerness in the mid-17th century was a short point of uninhabited marshland jutting out of the north-western tip of the Isle of Sheppey. Mariners referred to it as the Ness or the Point.
The Ness had strategic potential as it lay at the mouth of the River Medway -- up river at Chatham was the fleet anchorage. Whoever controlled the Ness controlled England’s warships.
Sheerness held potential for another reason. The three royal naval dockyards on the Thames and Medway – Deptford, Woolwich and Chatham – were all up rivers, away from the sea. Ships needing repair found the passage up river a tedious exercise which, for a large sailing ship relying on favorable winds and tides, could take days.
A similar problem existed for ships at the yards when they were ordered to put to sea. They had to negotiate the Thames or the Medway before entering the Thames estuary.
The Nore (a long east-west sandbank producing a large stretch of calmer water used by the navy as a convenient anchorage) lies just off the Ness. Ships anchored at the Nore in need of small repairs could carry out the work themselves; the crews used materials that were shipped down to them, occasionally employing shipwrights if more specialized tasks were involved.
Re-victualing could also be done from the Ness. Supplies were delivered from Chatham, or from Queenborough (the little Sheppey borough that stands on the banks of the Swale about two miles to the south of Sheerness Point). Likewise fresh powder and shot could be conveyed down river to the waiting ships.
When the second Anglo-Dutch war began in March 1665, the two enemies faced each other across the North Sea, dictating the likely arena for engagements, meaning ship maintenance would fall mainly to the dockyards of the Thames and Medway.
The Admiralty considered ways to overcome the problems presented by these river dockyards to aid quick turn-round of ships coming in for stores and repairs.
The Isle of Grain on the bank opposite the Ness was considered, as was Queenborough. Also contemplated was Sheerness, where the broad mudflats exposed at low tide on the southern side of the Ness had been used for the careening of ships' hulls. Sheerness was selected as the most suitable.
In the spring of 1665, a small ready-to-use victualing storehouse was erected adjacent to the foreshore near the Ness. As readily-available supplies of spare masts, yards, rigging and canvas came into demand to keep the fighting ships at sea, a stockpile of stores was developed at Sheerness in what rapidly became a ramshackle little depot.