More than a century after a soldier wrote a letter to his mother as he sailed to war and his death, it has been discovered in a bottle washed up on a remote beach.

Private Malcolm Alexander Neville's light-hearted note, penned on August 15, 1916, was found on Wharton Beach, near Esperance, about 750 kilometres southeast of Perth.

"Having a real good time," the letter pulled from inside a glass Schweppes bottle said.

"Food is real good so far, with the exception of one meal, which we buried at sea."

Pte Neville, who was killed in action in France in April 1917, aged 28, had departed Adelaide aboard a troopship three days earlier.

"The dear old (HMAT) Ballarat is heaving and rolling, but we are as happy as Larry," he wrote of the ship, which was later torpedoed and sank in April 1917.

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