I honestly didn't notice, but it may have. (Golly, I may have to go back and see it again!) Two other British actors (at least) also had noticeable roles in the movie: Orlando Bloom (Legolas in LOTR) as PFC Blackburn and Ewan MacGregor (Young Obiwan on Star Wars) as SP4 Grimes. MacGregor's accent was fine, but Bloom's accent was heavy on the English in the scene where he inprocesses into the Ranger company base.
Son, ev'rbudies accent chang's t' Texan eventually....
No, it was just an incredibly bad "southern accent" from the get-go. The guy's a more than decent actor...........but he was wholly incapable of affecting a proper accent (Texas, Georgia, Alabama.......it wouldn't have made any difference).
BTW, in case you didn't recognize him, that was the guy that played the despicable commander of the British Dragoons in "The Patriot". He did a fabulous.........if hammy..........job in that flick.