Coffin was 47 years old, and a temporary brigadier general, having been promoted to that rank temporarily in January 1917,[2] commanding the 25th Infantry Brigade during the First World War, when the following deed took place for which he was awarded the Victoria Cross for "most conspicuous bravery and devotion to duty".

[3][4] On 31 July 1917 in Westhoek, Belgium, Coffin's brigade had been shattered attempting to cross the marshy ground around the Hanebeek stream.

His very gallant conduct had the greatest effect on all ranks, and it was largely owing to his personal courage and example that the shell-hole line was held in spite of the very heaviest fire.

Throughout the day his calm courage and example exercised the greatest influence over all with whom he came into contact, and it is generally agreed that Brigadier-General Coffin's splendid example saved the situation, and had it not been for his action the line would certainly have been driven back".

[10] Coffin died in February 1959 and is buried at Holy Trinity Churchyard, Colemans Hatch, East Sussex.