The horrific meat grinder of World War One ’s Western Front produced an incredible number of outstanding poets --Wilfred Owen, Robert Graves, Rupert Brooke, Isaac Rosenberg, Walter de la Mare, Robert McCrae, Hermann Hesse, Erich Maria Remarque, Ernest Hemmingway among others. One, Siegfried Sassoon, was not only a genuine war hero, but used his fame and poetry to attack the prosecution of the war and defined the role of poet as political dissident.
Siegfried Sassoon was born in 1886 into a wealthy family in Kent, England. Sassoon led the life of a country gentleman of means. He attended Marlborough College and then went up to Clare College, Cambridge although he quit in 1907 before graduating.
Sassoon then spent the next eight years idling away his time hunting, playing cricket and golf, and writing poetry. He self published but received little or no critical attention.
When war began in 1914, Sassoon joined the Sussex Yeomanry on the first day of the war. He later transferred to the Royal Welch Fusiliers as an officer in May 1915, where he met Robert Graves. 
Initially eager to go to war, the death of his brother at Gallipoli in 1915 and his friend Rupert Brooke on the passage to the middle east, saw Sassoon quickly become disillusioned with the war. He began to take on almost suicidal missions and earned nickname 'Mad Jack' for his fearless courage in leading night raids on German trenches. He was awarded the Military Cross in June 1916 for assisting a wounded man back to British lines while under fire and was wounded in April 1917. Sent back to England for recuperation, Sassoon published a collection of anti war poetry called “The Old Huntsman” and a letter in The Times, claiming that the war was being deliberately and unnecessarily prolonged by the government. The letter was read out in Parliament and became a minor scandal.
The army sought to try Sassoon for insubordination but Graves managed to convince a military review board that Sassoon was suffering from shell shock. Sassoon was sent to Craiglockhart military hospital to recover where he met fellow patient and poet Wilfred Owen. Sassoon subsequently edited and arranged publication of Owen's work after the war.
Discharged from Craiglockhart, Sassoon and Owen returned to France. Sassoon was wounded and sent home while Owen was killed in the last week of the war. Back in England, Sassoon published “The Counter Attack” in 1918.
After the war, Sassoon wrote poetry and toured England the US giving lectures and readings before embarking on series of fictional works loosely based upon his immediate pre-war and war experiences: Memoirs of a Foxhunting Man (1928), Memoirs of an Infantry Officer (1930); and Sherston's Progress (1936).
He followed these with three volumes of actual autobiography: The Old Century (1938); The Weald of Youth (1942); and Siegfried's Journey (1945).
Siegfried Sassoon died in 1967.

Aftermath

Have you forgotten yet?...
For the world's events have rumbled on since those gagged days,
Like traffic checked while at the crossing of city-ways:
And the haunted gap in your mind has filled with thoughts that flow
Like clouds in the lit heaven of life; and you're a man reprieved to go,
Taking your peaceful share of Time, with joy to spare.
But the past is just the same-and War's a bloody game...
Have you forgotten yet?...
Look down, and swear by the slain of the War that you'll never forget.

Do you remember the dark months you held the sector at Mametz--
The nights you watched and wired and dug and piled sandbags on parapets?
Do you remember the rats; and the stench
Of corpses rotting in front of the front-line trench-
And dawn coming, dirty-white, and chill with a hopeless rain?
Do you ever stop and ask, 'Is it all going to happen again?'

Do you remember that hour of din before the attack--
And the anger, the blind compassion that seized and shook you then
As you peered at the doomed and haggard faces of your men?
Do you remember the stretcher-cases lurching back
With dying eyes and lolling heads-those ashen-grey
Masks of the lads who once were keen and kind and gay?

Have you forgotten yet?
Look up, and swear by the green of the spring that you'll never forget.