THE SOUNDS of birdlife and gunfire might reasonably characterise the Thames estuary over the last three or four centuries. As time has gone by they've been successively overlaid with new arrivals – paddle steamers, ships' hooters, aircraft, scrambler bikes – but there are still birds around and people still go shooting.

Shornemead Fort was built in the 1860s on the Kent side of the estuary about a mile-and-a-half east of Gravesend. The Army demolished most of it in the 1960s, leaving only the casement facing the estuary and some bits of wall to the sides. Anyone can explore the fort and no attempt has been made to preserve what's left. Layers of colourful grafitti have been added to those surfaces which are sufficiently smooth.

Inside Shornemead Fort.

The bangs and pops you can hear in the recording might have come from the Metropolitan Police firing range to the west, but there are also clay pigeon ranges at points along the estuary beginning at Dartford Marshes. In former times, Shornemead Fort might have added the occasional thunder of its cannons during gunnery practice. It also marks the site of an earlier battery constructed towards the end of the 18th century, which you can see highlighted in yellow in the First Series Ordnance Survey map below. This dates to around 1805.

First Series Ordnance Survey map showing Thames forts and batteries

The map shows the other forts and batteries of the day, although curiously omits New Tavern Fort at Gravesend. The battery on the Kent shore, towards the top right-hand corner, fell into disuse by the middle of the 19th century and was converted to a pub, the Anchor & Hope. No obvious trace of it remains today. Tilbury Fort, in contrast, has been well preserved and is now owned by English Heritage.

Much further to the east is my favourite of all the surviving estuary forts, the Grain Tower. Originally built in the 1850s, it's situated at the mouth of the Medway between the Isles of Grain and Sheppey. The Tower's regular isolation by the tides raises all kinds of imaginings: scrambling onto it and living there surreptitiously before declaring your own miniature polity, like the Principality of Sealand.

Grain Tower.

It is not the estuary's militarised history which encourages thoughts of boundaries and territories. Rather, it is the general scruffiness and sense of absent ownership from which springs the mirage of finding your own tiny off-grid niche, like the houseboat communities lurking in the creeks at the north of Canvey Island and on the Swanscombe peninsula.

As with the sea walls, state power projected as forts and batteries betrays uncertainty over the land's resilience. A chain of warning beacons had been established along the estuary during the 14th century, but they didn't prevent a joint French-Spanish raiding part from attacking Gravesend in 1380. Around the middle of the 16th century, Henry VIII ordered artillery blockhouses to be built between Gravesend and Higham, fearing attack from Catholic Europe.

Such defences were too far upstream to prevent incursions during the Anglo-Dutch War of 1667, when the Dutch captured the fort at Sheerness and attacked the English fleet where it lay at anchor on the Medway. They also found time to send a small raiding party to Canvey Island, where they burned down some houses and barns, and stole sheep to add to their provisions.

The firing of naval and shore cannons during such confrontations would have been audible far upstream. In 1665, Samuel Pepys wrote how the guns at the Battle of Lowestoft were heard in London, principally by watermen working amid the relatively quieter surroundings of the Thames mid-river. A few years earlier he noted the effects of cannonfire during gunnery practice by frigates at Tilbury:

Early in the morning at making a fair new establishment of the Fleet to send to the Council. This morning, the wind came about, and we fell into the Hope, and in our passing by the Vice-Admiral, he and the rest of the frigates, with him, did give us abundance of guns and we them, so much that the report of them broke all the windows in my cabin and broke off the iron bar that was upon it to keep anybody from creeping in at the Scuttle.

Over time, the sounds of explosions and large guns were confined further and further eastwards along the estuary, now emanating solely from the Ministry of Defence's ranges on Foulness Island. A forthcoming activity webpage categorises the sounds as local gunfire, gunfire and explosions, depending partly on how far away they can be heard.

The same pattern must hold for the smaller guns of wildfowlers, once heard in the marshlands of the Greenwich peninsula and the Isle of Dogs, the latter a lingering southern extension of the Stepney Marsh. In the late 19th century, the proximity of Benfleet station made Canvey Island popular with sportsmen. As the writer and broadcaster James Wentworth Day recalled in his 1949 book Coastal Adventure:

Nearly every fisherman carried an old muzzle-loader, while the boom of punt guns rolled in muffled echoes up the coast in the dim light of winter mornings. Big bags of fowl, both duck and geese, were got on Benfleet Creek and at Deadman’s Bay.

A stalking horse depicted in the Illustrated London News

The picture above is taken from the Illustrated London News of 1874 and depicts hunters by the Thames, as well as the origin of the term 'stalking horse'. Wildfowling is now regulated through a permit system and it's more extensive on the south side of the estuary, where the local wildfowling association is the biggest private landowner in North Kent.