Found what that poem was called.
I don't suppose anyone anctually cares. But it's being pasted here anyway ^_^
War exalts and cleanses: it lifts man from the mud!
Ask God what He thinks of a bayonet dripping blood.
By War the brave are tested, and cowards are disgraced!
Show God His own image shrapnel'd into paste.
Fight till tyrants perish, slay till brutes are mild!
Then go wash the blood off and try to face your child
"War Exalts" (1918) - Harold Begbie