William Allan was born in Methven, Perthshire in 1898.

In 1901 the Allan family were living at Logiealmond Road, East Busby, Methven. William's father, 43-year-old John, was a farmer and his mother Jessie was 28. William had an older brother named Alexander and a younger sister named Jessie. Also living in East Busby with the Allans, was Margaret Lister the family's general domestic.

As soon as he was old enough to sign-up (around December 1917) William Allan joined the 27th Battery, Royal Field Artillery (RFA).

At this time William's battery was in position near Monchy-le-Preux in northern France. 

In February 1918, the Battery were at Fampoux firing on Roeux and at the end of March, it retired to a new position south east of St Lauren Blangy.

In August 1918, the Battery moved to Monchy-le-Preux, where considerable shelling and several successful barrages took place. In early October the Battery moved into four old German gun-pits one mile north west of Cambrai. Although there is no definitive record of where, or how William Allan lost his life, he died of wounds probably sustained during this period in Cambrai.

He was buried in Terlincthun Cemetery which was used chiefly for burials from the numerous base hospitals and medical facilities in the area. He was 20 years old.

The Allan's local newspaper, The Perthshire Constitutional, posted this notice:

“Gunner William Allan, second son of the late Mr. John Allan, Farmer, West Cultmalundie, died of wounds received in action. He assisted his father on the farm up till Martinmas 1916, when he joined up and went into training at Bedford. He had seen eleven months’ active service at the time of his death. He was of a bright, cheerful disposition, and greatly liked by his fellows. His loss is mourned by many.”

Gunner 193174, William S. Allan of the 27th Battery, 32nd Brigade - Royal Field Artillery, who died on the 25th of October 1918, lies at rest in the  Terlincthun British Cemetery, on the northern outskirts of Boulogne. The personal inscription on his headstone reads "Second son of the late John Allan of West Cultmalundie Perth."

William Allan is also commemorated on the Methven Parish War Memorial, the Methven United Presbyterian Church War Memorial, the Methven Parish Church War Memorial and the Logiealmond Parish Church War Memorial.