Siegfried Sassoon and Wilfred Owen both were fairly truthful in their war poems. They described it vividly and called it "hell" in the face of patriotism and duty to country. Sassoon's "The Rear-Guard" and Owen's "Dulce et Decorum Est" are good examples of this.
There were others, however, who hid the gruesome truth of war and idealized everything for the people back home. Rupert Brooke's "The Soldier" is a good example of this type of poet who glorified war and what is stood for in order to stir up feelings of honor, duty, and loyalty to country.