Hidden Camo

Simply use the pelecan grenade trick to get to the top of the level (to see the marine), but instead of heading towards the marine, head the opposite way, hugging the edge, until you see the strange plant you climb onto to cross over to where the structure is, instead, aline yourself with the tail of the plant, and look down, there will be a pipe, jump down onto it, and walk into the bush, you have just walked into a hidden active camo.