
Charles Bean would have to be up there for getting close to the action (he landed at Anzac Cove at 10am on 25th April 1915, just 4 hours after the first landings and spent probably more time at or near the Western Front than almost any other Australian soldier), and relaying it in a way that the average civilian at home as well as the digger in the trenches could relate to. He wrote volume I through VI of the 12-volume
Official History of Australia in the War of 1914–1918 and was instrumental in setting up of the Australian War Memorial. Without Bean, there would be no ANZAC legend.
Walter Kronkite might get a guernsey, though I'm not that familiar with too many of the American correspondents work to comment knowledgeably.