Winslow Homer painted cinema before cinema. The lone sailor slumped exhausted on his broken boat as sharks circle, not yet noticing a ship on the horizon. A military rifleman perched on a thin branch, balancing his barrel as he lines up a kill shot. A maiden held aloft by a winch, wet clothes clinging to her body above the sucking waves, in the arms of a daring lifeboatman. This is thrilling stuff – drama, heroism, romance, sex and peril.

Homer started his working life on the popular press (where we know a thing or two about titillation and amping up the drama). Commissioned to produce eyewitness drawings for Harper’s magazine, Homer was embedded on the Union side during the American Civil War (1861-65). He reported from the front line, sketching flattened battlefields, sharpshooters and prisoners.

His sketches – and the prints made from them – are not in the National Gallery’s handsome survey exhibition. On show instead, in its first gallery, are the paintings that followed them: colour elaborations of his widely circulated war coverage. Canvases that reflected America’s heroism – and its pain – back at itself.

Homer was not an impartial witness. He was invested in the Union cause (Harper’s supported Lincoln and the abolition of slavery). He was also invested, more broadly, in the reconciliation, reconstruction and nation-building it was hoped might follow the conflict.

In Prisoners from the Front (1866), a ramshackle clutch of Confederate captives – a farmhand, a grey-bearded old man in civilian clothes, a rifleman and a long-locked officer – line up on a denuded battlefield before a Union cavalryman. Homer portrays all five as heroic figures, binding these soldiers from opposing sides together through the non-hierarchical arrangement of the figures, and a gaze held by the two officers.

Wrought into a simple image of rural labour – a man in shirtsleeves scything golden wheat – The Veteran in a New Field (1865) is seeded with symbolism of wholesome rebirth and nation-building. On the stubble in the foreground is a military jacket – this farmer has thrown off the trappings of combat to work the land.

Homer returned to the southern states to observe the lives of formerly enslaved black labourers. In the supremely awkward A Visit from the Old Mistress (1876), three black women in patched working clothes – one holding a young child – gaze warily at an older white woman in a rich black dress with a lace collar. No one in the picture wants to be there. As in Prisoners from the Front, Homer has arranged the women in a line, suggesting equal status, but here with an undercurrent of distrust and resentment running in both directions.

In The Cotton Pickers, painted the same year, Homer instead romanticised black labourers. Two beautiful young women are positioned in a pale field, their bodies rising between soft cotton heads, set against the blushing clouds of the evening sky. Homer paints the women sombre, but at ease: they are staunch, yet there is softness to their gestures as they carry their great baskets in at day’s end. The work was bought by a British cotton merchant – a comforting illusion of gentle rural labour.

Travelling to England in 1881, Homer ended up at Cullercoats on the North East coast. He spent 18 months in this fishing village in which human drama of the sea played out with tragic frequency. Homer was aware of JMW Turner’s work: Prisoners from the Front was purchased by a collector who also owned Turner’s Slave Ship (1840).

At Cullercoats he studied sea and sky, the movements of boats on the waves and steadfast working women. His grandest Cullercoats paintings are narrative epics. He brings us a windswept mother, babe in arms, staring out over the lashing ocean.

Homer also studied the technology of seafaring. In Eight Bells (1887), we join sailors on deck after a storm, their oilskins slick with water as they check instruments and adjust their course. Skilful as they are, many of these paintings are unashamedly sentimental, in a way that can be jarring to the contemporary viewer. (Studying Homer’s muscular working women, I couldn’t help thinking of the heroic labourers of socialist realism.)

There is a distinct eroticism to his work. It is there in the gaze held between the handsome Union and Confederate officers in their tight uniforms in Prisoners from the Front. In Undertow (1886) a pair of muscular male rescuers, their sculpted torsos slick with spume, draw two long-haired young women back to the shore from a churning ocean, their wet robes clinging tightly to their rounded buttocks and breasts. It’s a painting about peril, the threat of death at sea, the wild and uncontrollable power of nature. But it’s also a sexy painting: these are bodies to be enjoyed. It’s pure Hollywood.

All those elements are at play in The Gulf Stream (1899), named for the swift current propelling North Atlantic trade routes. A muscular black man, stripped to the waist, lies on the deck of a small boat. He has steered out of a tropical storm – still visible in the background – but his mast has broken, and his sail is sliding into the water. Sharks boil up through the water, rubbing their backs against the tilting hull of the boat. Strewn across the deck, sugar canes remind us that this is an active and important trade route: the dangers the sailor faces menace all who work the Gulf Stream. In the background a ship is visible – an emblem of hope.

The Gulf Stream has been interpreted in many ways. It’s an enigmatic work, the symbolism of which can be bent to serve many causes. At heart, though, it positions a heroic man alone against the wild cruelty of the natural world. This is a figure that reappears in many guises in Homer’s paintings: he is the young boy pulling a shot deer into his canoe on a swollen river, the tracker out in the winter wilds with a shotgun for company, the sailor trying to propel a huge trunk of driftwood on to land to heat himself for the winter. This celebration of the heroic American gunslinger out in the (supposedly unpeopled) wilds makes Homer a curious choice of artist to be celebrating in this moment. There are gunshots behind much of the drama in his paintings.

In Right and Left (1909), painted a year before his death, one of a pair of wild ducks rising out of the water is shot by a distant figure on a canoe. It’s an extraordinarily stark painting.

Homer’s compositions became more graphic and refined, and his interest in seascapes and the play of light more intense as he grew older. In Kissing the Moon (1904), the lower right third of the painting is eaten by a dark wave that obstructs our view of sailors out at night in a small boat. A painting of Cape Trinity by moonlight from the same year is a near abstract study in greys and blacks.

Homer’s eye for drama made him the most celebrated American artist of his day. By the end of his life, he was looking for it not in human subjects, but in the elements.

Winslow Homer: Force of Nature is at the National Gallery, London, until 8 January

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