Start with what you already know

Before you open a single record, gather everything the family already holds. A full name is only the beginning: an approximate date of birth, a birthplace, a trade, a middle name or a distinctive address can separate your soldier from a dozen men with the same name. Photographs are quietly useful here, since a cap badge or a shoulder title will tell you the regiment or corps he served with. So will memorial cards, inscribed pocket watches, a discharge certificate tucked in a drawer, or a letter sent home from a training camp. Ask older relatives now, while you still can; half-remembered details about "Uncle Ted who was in the artillery" are often the thread that unravels the whole story.

Three facts matter more than any others when you begin searching: the regiment or corps, the service number, and the date he first went overseas. Everything else can be built around them.

Why First World War records are patchy

Anyone tracing a soldier of 1914 to 1918 soon learns the hard truth about the archive. In 1940, enemy bombing destroyed the great majority of the army's service records for other ranks — roughly two-thirds of them. What survived became known as the "burnt documents": pages singed at the edges, water-stained and sometimes barely legible after the firefighting. A smaller set of records, often called the "unburnt documents", survived because they were held elsewhere, largely concerning men discharged to a pension or who died in service.

Officers' files fared much better and are far more complete. For other ranks, though, the golden rule is that an absent record proves nothing. Your soldier may simply be one of the many whose papers went up in smoke. Persistence, and a willingness to use indirect sources, is everything.

Service records: the heart of the matter

When a service record does survive, it is a remarkable thing. Look first at the attestation papers, which usually give his age, height, chest measurement, complexion, eye colour and any distinguishing marks, along with his occupation, home address, marital status and next of kin. From there the file follows him: postings between battalions, promotions and reductions in rank, courses attended, medical sheets listing wounds and illnesses, and finally the date and reason for discharge, whether through wounds, sickness, the end of his engagement or death.

• Note the difference between the date he attested and the date he was mobilised — Territorial Force men often enlisted years before the war and were embodied in August 1914.
• Watch for changes of regiment. A man might move from an infantry battalion to a labour corps, and his service number would change with him.
• Disciplinary entries are common and human: absence without leave, drunkenness, a lost kit. They tell you as much about a man's war as the medals do.
• Some soldiers served under an assumed name, which explains many a missing record.

Medal rolls and index cards

Medal records are the great substitute for lost service papers, because they cover almost every man who served overseas. The medal index card is the place to start: it gives regiment, rank, service number, the first theatre of war he entered and the date he arrived there, plus references to the relevant rolls. That arrival date is invaluable, since it tells you which campaign medals he qualified for and, by extension, when he left Britain.

The standard pair were the British War Medal and the Victory Medal. The 1914 Star and the 1914–15 Star went to those who arrived early enough to see the opening campaigns, and the Territorial Force War Medal to certain Territorials who served overseas before 1916. If no medal card exists, it usually means the man never left the United Kingdom — useful evidence in itself, particularly for men who died of illness at home.

Also worth seeking out are the Silver War Badge rolls, which record men discharged through wounds or sickness and give enlistment and discharge dates, age and unit. They can plug gaps where a service record is missing.

War diaries: putting your soldier in context

War diaries were kept at unit level, not by individuals, and they are the closest most families will get to a day-by-day account of the war. A battalion diary records the weather, the moves, the trenches occupied, the shelling, the raids and the casualties, often with appendices of operation orders, maps and casualty returns.

Use the dates in the service record — a wounding, a promotion, a period in hospital — to find the right weeks in the diary. Your soldier's name will rarely appear unless he was an officer, but the diary will tell you what he lived through. Reading "heavy shelling on the support line" when you know your great-grandfather was wounded that very week is a sobering experience.

Filling the gaps and reading between the lines

Where the official record fails, a constellation of other sources takes over. Soldiers' wills survive for many who died on service and often name family members and addresses. Local newspapers, now widely digitised, printed casualty lists, letters from the front and reports of men home on leave. War graves records identify the cemetery or memorial for the fallen, and the registers sometimes include personal inscriptions chosen by families. Absent voters lists from 1918, church and workplace memorials, rolls of honour and school magazines all place a man in his community.

Build a timeline as you go, and accept that some gaps will never close. The pleasure of this research lies in the accumulation of small certainties — a date, a place, a name — which together turn a silhouette into a person.