Throughout the poem ‘Dulce et Decorum Est’ the poet has used vivid imageries to portray the real condition of the soldiers in the First World War. These imageries are not imaginary but based on real experience of the poet as he himself served in the war as a lieutenant.
 
The poem starts with the description of the tired, war-ridden soldiers. “Bent double, like old beggars under sacks,/ Knock-kneed, coughing like hags“. This image of soldiers are in complete contrast of what common people have in mind — some brave heroic men boldly facing and winning over every challenges before them. The poet deliberately presents such images of the warriors to shatter the romantic ideals of people regarding wars and so-called war-heroes. The expressions like “we turned our back”, “many had lost their boots, but limped on, blood-shod”, “drunk with fatigue” — all present clear images of the soldier in horrible conditions. 
 
The second stanza depicts a victim of a gas attack. It was probably chlorine gas making a “green sea” in which the speaker saw his fellow soldier drowning as he was “yelling out and stumbling, and floundering like a man in fire or lime…”. 
 
The third stanza presents an imagery of the dead soldier when his body was being taken away in a wagon. His “white eyes writhing in his face”, “his hanging face”, the blood jolts “gargling from the froth-corrupted lungs” — all are expressive of the tragic situation the soldiers have to face in war. 
 
So, imagery is the device the poet has employed in the poem ‘Dulce et Decorum Est’ to convey his anti-war message. And it has been more effective than stating his views in a straightforward manner.