What do we know of great-uncle George Chrystal?

That he was an only son, elder brother of four sisters living in Edwardian comfort at Bloomhill House at Cardross. That he was a territorial soldier sent to France as a lieutenant in the 1/9th (Dumbartonshire) Battalion, Argyll And Sutherland Highlanders, following Germany's attack on Belgium in August 1914. That he was an Oxford graduate, an eligible bachelor, a not excessively martial but dutiful part-time officer.

We know he was killed aged 29, perhaps by one of the Western Front's first gas attacks, somewhere in the woods near Bellewaarde Lake at the end of the Second Battle of Ypres, on May 25, 1915. We don't know – and never will – where Geo (pronounced Joe) is buried, or even if he was. We do know his name is on panel 42 on the Menin Gate at Ypres.

We also have his letters, preserved in a tan leather folder by my great-grandmother who, like so many widows, never recovered from his loss. She retired to darkened rooms, imposing his ghost on her too-young grandchildren in a manner considered morbid by some contemporaries.

Geo's niece, my aunt Mary, born within a decade of the Armistice in 1918, has lived with his heroic absence since childhood. I have been editing his letters, and planning a disabled ex-servicemen's housing project at Bloomhill in his memory. With Remembrance Sunday approaching, we felt a visit to Ypres – Ieper as its Flemish-speaking residents prefer – was an overdue gesture to Geo, our way of showing he was still remembered, even loved, in an abstract way.

On the BMI flight from Edinburgh to Brussels we perused the collection of 40 neatly written letters and postcards to "Moth and Fa", dating from August 17, 1914, when Geo left from Stirling for training at Bedford, transferring to France in February 1915, then to the bulge in the Flanders front line known as the Ypres Salient.

The letters reveal Geo to be a conscientious leader to "the men", mostly industrial workers from Dumbarton and Clydebank. Apart from in the heat of battle, officers, of course, had it relatively easy. To contemporary ears there is a touch of Blackadder Goes Forth in his repeated thanks for the pheasants, port, champagne, haggis, chocolate, "toffee biscuits", hard-boiled eggs and other luxuries with which he was showered by family and friends: "I got the shirt, towels and woolly slippers, which are splendid for wearing in the evening". There is a surreal contrast between these comforts and Geo's life in the mud of Flanders. For all their privileges, officers – including Geo's battalion commander, Colonel James Clark, an Edinburgh barrister – were mown down and gassed as efficiently as other ranks, 431 officers in the Argylls alone.

Geo was neither jingoistic nor a disillusioned critic of the futility of it all (he didn't live long enough). His letters home remain heroically jaunty: "It is the German custom to give the British troops who relieve the French a pretty warm reception – we certainly came in for it this time"; "nothing much to do thro' the day, & trench digging by night - nothing to grouse about".

Geo's sanitised accounts could not disguise the darkening awareness of a new kind of war, one that revealed itself with massive casualties from the bombardment and gassing. The Imperial War Museum describes the Second Battle of Ypres, in which 105,000 died in the only major German offensive of 1915, as "particularly brutal and savage, fought in anger and without compassion or quarter". Geo calls it "a horrible business altogether, which one has to do one's best to forget".

"Dear Moth" he writes on May 12, two days after 300 men and 12 brother officers were killed, "I am so sorry I haven't been able to write sooner & hope you have not been very much worried. The scrapping here has been too strenuous for the post to go with any regularity. I'm afraid you will gather from the casualty lists what a tough time we have had. It really has been awful, but I think & hope that the worst of the business as far as we're concerned is now over & that there is a chance of us being relieved quite soon."

We were based at Ieper's central Novotel Hotel. There, we brought order to the scraps of information accrued over the decades, fitting mental pictures to some charged words: Hill 60, Langemark, St Julien, Kitchener's Wood.

The Flanders government is planning a series of events to mark the centenary of the start of the "war to end all wars" in October 2014, honouring the generation whose grip on the collective conscience seems only to strengthen. Flanders is investing €50m in anticipation of a 30-40% increase in the annual 350,000 "peace tourists".

Visits to the battlefields are now the stuff of routine school trips – maybe compulsory ones, according to a recent suggestion by David Cameron, the Prime Minister, though neither my aunt nor I had ever been on a battlefield tour.

Centred on the Grote Markt, Wipers (as Commonwealth troops called it) was flattened by repeated bombardment while Geo was at the front, images of its smashed carcass having the same impact on his generation as those of Hiroshima did a generation later.

Modern Ieper has reconstructed Gothic architecture, ancient fortifications and attractions such as the Belle Almshouse Museum and Merghelynck Hotel-Museum, which recall centuries as a prosperous medieval trading hub. But the intensity of fighting in 1914-18 (there were five separate Battles of Ypres) mean it is fated to be the hub of the battlefield tourist trail following the line of trenches stretching 450 miles to the France-Switzerland border.

The medieval Cloth Hall, or rather the reconstruction made at German expense in the 1920s, still dominates the town, and holds the In Flanders Fields Museum, the best starting point to any visit.

According to the letters, Geo and his men were billeted in the relative comfort of a "sort of nunnery", until it was blown to bits. He expressed a rueful affection for Wipers. "I don't fancy we shall be billeted there again," he writes. "It is a pity – life there was comparatively civilised, and there was quite a decent 'coiffeur' if one cared to wait 2 hours for a haircut. I haven't had my clothes or boots off, nor had a shave for over a week & we are a dirty looking crew."

Nowadays the knowledge that German resentment over reparations helped cause the Second World War casts a shadow on the placid, brick-built town, but its recovery has a more uplifting message, best contemplated in the autumnal early-morning light along the 17th-century ramparts, now a kind of circular park.

I won't easily forget coming across the clean, pale ranked gravestones of the Ramparts Cemetery by the Lille Gate on an early-morning jog; impeccably kept, like all Commonwealth War cemeteries, its lawn sloping down to the moat.

A similar emotional punch was the first sight of the Menin Gate, built over the road along which men marched to the Front. Caught in the evening sunlight, this stretched neo-Classical arch, grand but not pompous, was built in 1921 by Sir Reginald Blomfield, the Elgar of Edwardian architecture. It contains the names of the 55,000 Commonwealth soldiers who have no known grave. We returned for the Last Post – a bugle ceremony held at 8pm every night since 1928 which attracts huge crowds, especially around Armistice Day. It was easier than expected to find Geo's name under the Argyll And Sutherland Highlanders: Lieutenant GG Chrystal. We slipped a Scottish poppy into a groove in the masonry.

That day we had spent the afternoon with Lest We Forget Tours, one of several companies specialising in battlefield tours. It is hard to conceive of a better one than this, led by a former Royal Tank Regiment NCO, Chris Lock. A Flemish speaker who has lived here for years, Lock has an intimate knowledge of the battles and deftly improvised a trip tailored to what I was able to tell him of Uncle Geo's service and death.

Lock had a dramatic, empathetic way of bringing the action to life, and of transporting us imaginatively as well as literally to the field of battle. Lock is accustomed to elderly visitors and, conscious of my aunt's advanced age, he took us to the Essex Farm Dressing Station, on the Yser Canal, one focus of the Second Battle of Ypres (April-May 1915) and a good guess as to where Geo met his end. It was the final phase of a battle that started in panic following the German release of chlorine gas, the first time chemical weapons were used on the Western Front. "We had a little taste of the 'poisonous gas' business," Geo writes home on May 18, "and one or two men were laid out by it. We all had to wear wet respirators" – wet with urine, he doesn't add – "which are some protection against it – even the little we had made one's eyes very sore."

The only good thing to be said about the decimation of the 1/9 Battalion Argylls at the end of this battle was that they were spared its sequel, better known as Passchendaele, two years later (June-November 1917). Geo's battle, although one of the bloodiest of the war, was at least short.

The muddy carnage of Passchendaele ranks with the Somme (July-November 1916) as a symbol of futility. A short drive from Ypres lies the flint-walled Tyne Cot ceremony, with its 35,000 graves, the largest Commonwealth cemetery in the world, next to it a sleek modernist visitor centre commanding the crest of the gentle rise for which so many lives were lost.

Passchendaele's story is told in a museum in the village of Zonnebeke a few miles from Ypres. Here, the basement is a recreation of a dugout, the wooden-walled underground complexes, infested with rats, in which men lived for months.

The horror these interpretative centres conjure up contrasts with the flat, quiet, timeless Flanders countryside and its dead-straight, tree-lined roads running between the boxy red-brick farms and hamlets.

In a letter written three weeks before his death, Geo takes note of this surreal contrast between serenity and violence. "There's really no news that I'm allowed to give so I will stop. It must be lovely at home just now, we all get beastly homesick at times and the spring seems to make it worse. This wood is a queer mixture of green leaves, violets, nightingales and shells – but we might be much worse off than where we are."

His last letter, dated May 23, two days before his death, is brief and bland, thanking his mother for the "shaving tackle of a very superior kind! And also a mixed lot of eatables & cigarettes which arrived today + clean shirts, socks etc - I'll write again as soon as poss."

The story of what then happened in that wood is taken up in a surviving soldier's record, displayed in the Argylls' regimental museum at Stirling Castle. "We were up against overwhelming odds for days, the Germans were trying to break our lines. The 9th kept up a brisk rate of fire on the advancing Germans who lost a terrible amount of men but we ourselves lost heavily. The wood was raked by shelling which seemed to scorch every yard of it - trees were smashed like matches. When the shelling ceased hardly a tree remained standing, all was a jumble of broken timber beneath which lay dead men, broken rifles, equipment and torn sandbags."

Reading the letters of one of those long-dead men, close to where they were written, cuts through the intervening 100 years. Never consciously heroic, Geo might be surprised – and gratified – at the enduring potency of his and his comrades' deaths. Or rather of the lives they didn't get to live. n