He served in World War I with the First Australian Imperial Force and was killed in action in the mounted charge of the 4th Light Horse Brigade at Beersheba in Ottoman Palestine.

[3][4][5][6][7] Although only 5'8" (173 cm) tall—the same height as Harold Larwood—he was arguably the best fast bowler through the first decade of the 20th century,[8][9] he had a reputation for breaking stumps.

While regarded as the fastest of his era in Australia (his pace saw him nicknamed "'Terror' Cotter" by English fans) he did not always have the control to back it up, hitting W.G.Grace on the body with a full toss on his first tour of England.

Despite having no great riding ability, he was accepted into the 1st Australian Light Horse Regiment; he took a late part in the Gallipoli campaign.

While serving in the AIF, he participated in a unique Australia v. England "Test Match" played in 1917 between two teams made up from the Australian and British troops stationed in Palestine.

[20]At the end of the charge, as troops dismounted to engage the enemy, a Turk shot Cotter dead at close range.