Jackson was a sniper The US did have an official role for snipers in WW though it was a different one than the current more fieldcraft based version that you are thinking of Note the scene where Caparzo gets shot Jackson points out the church and says Thats where I would be and sets up for a sniper kill on the target Because he DOES have a knowledge of sniper tactics Jackson is clearly a sniper rather than a dedicated marksman a role that did not exist in WW  Son of the Defender