He was 34 years old, on 14 September 1914 during the Race to the Sea at Missy, France, in the First World War, he performed an act of bravery for which he was awarded the Victoria Cross.

His citation read: At Missy, on 14th Sept., under a heavy fire all day until 7 p.m., worked with his own hand two rafts bringing back wounded and returning with ammunition; thus enabling advanced Brigade to maintain its position across the river.Johnston afterwards served with the tunnelling companies of the Royal Engineers at St Eloi in the Ypres Salient.

The Germans exploded mines under the area known as The Mound just south-east of St Eloi in March 1915 and in the ensuing fighting the British suffered some 500 casualties.

A month later, on 14 April 1915, the Germans fired another mine producing a crater over 20 metres (66 ft) in diameter.

[3] Johnston left 172nd Tunnelling Company in early May[4] and was killed in action at Ypres on 8 June 1915.