Sir Arthur Streeton (1867-1943) is best remembered in Australian art through his association with the so-called "Heidelberg school" where, in the late 1880s and early 1890s, a number of young artists painted in the Heidelberg and Eaglemont areas on the outskirts of Melbourne. Here the painters combined nationalism, naturalism and a timid application of some aspects of impressionism to paint images of the quintessential Australian landscape with generous doses of juvenile romanticism.

Although Australian-born, Streeton, like so many artists of his generation, sought recognition in the "mother country" and sailed for London in 1897. On his several trips to England, he failed to replicate the success he experienced in Australia, although he did exhibit at the Royal Academy, the Paris Salon and was a member of the Chelsea Arts Club. Together with his friend and fellow member of the Chelsea Arts Club, Tom Roberts, Streeton, at the age of 48, with patriotic zeal, early in the Great War, joined the Royal Army Medical Corps (British Army). He was stationed at the 3rd London General Hospital in Wandsworth, where he worked alongside other Australian artists, including Roberts, A. Henry Fullwood and George Coates.

Streeton was appointed an official war artist in May 1918, holding the rank of Honorary Lieutenant, and was sent to France attached to the 2nd Division AIF. He worked mostly around the Somme battlefields until mid-August 1918, when he returned to London. Between October 17 and November 20, 1918, Streeton returned to France, again with the 2nd Division, but this time he focused on the destruction around Peronne.

The important exhibition at the National Gallery, curated by Dr Anna Gray, examines Streeton's work predominantly on the battlefields of France, in many instances observed as watercolour drawings on the spot and later realised as finished paintings in his studio in London. The show is being held in the centenary year of Streeton's World War I art.

Streeton was an unconventional war artist; he was less concerned with the heroics of the battlefront or the movement of armies and battleline strategies, but was fascinated by the aftermath of battle and the scars that it inevitably leaves on the landscape and buildings as well as on people. There is a remarkable painting, Troops bathing, Glisy, 1918 with an idyllic and tranquil setting of naked men swimming in a river east of Amiens with the forest trees beautifully reflected in the water. At first glance, you almost fail to notice that a shell has just landed and exploded in the water and there may be further shells travelling in the sky. It is as if war has brought death to Arcadia.

Streeton combines his lyrical gifts as a landscape artist, to observe the setting with all of its charming details, and those of a narrator, who tells of unexpected occurrences, such as observation balloons being shot out of the sky and allied troops plunging to their deaths in an otherwise idyllic setting. Other memorable paintings include the war-scarred Amiens cathedral, shown in a gorgeous light-filled breathing watercolour painting as well as a heavier and more resolved finished oil painting. There are also several paintings based on the battlefield around Mont St Quentin where again tranquillity carries the scars of barbarity.

Streeton at one stage observed, in a letter to Sir Baldwin Spencer: "True pictures of Battlefields are very quiet looking things. There's nothing much to be seen – everybody & thing is hidden & camouflaged – it is only in the Illustrated papers one gets a real idea of Battle as it occurs in the mind of the man whose never been there."

The strength of the exhibition, as well as Streeton's art at this time, lies in the watercolours, many of which appear full of light and possess a freshness of touch, despite the somewhat oppressive subject matter. These include the Ruins in Peronne, 1918, Mont St Quentin, a sketch record for Sir John Monash, 1918, Prisoner-of-war compound, Abbeville, August 1918, and Mont St Quentin, October 1918. Streeton in his war art has the genius for the understated, where some grim detail awaits the viewer like a hidden emotional assassin. We may be seduced by the wonderfully painted expanses of barbed wire and only in the distance catch a glimpse of the dark shapes of inmates, or see the ruins of some building full of luminosity and later notice papers scattered on the floor of a life extinguished.

Although Streeton may be one of Australia's best-known artists, this exhibition reveals a lesser-known aspect of his art, one where a social conscience emerges and the landscape is no longer purely a celebration of pastoral wealth, but it also carries a lament about loss and violence. After the war, when Streeton returned to Australia, he again turned to the landscape and painted the Grampians and the Dandenong Ranges, but now frequently making an environmental statement about deforestation and the destruction of Australia's biodiversity.