Darkest Of Days

This can be done on the WW1 mission "Germans on run". There is a river you will come across during one of your objectives (right near the end of the level) Run into the water and keep walking in the water. You will find a spot where you can completely submerge in the water. Right after you die it will pop, just as you are given the you have died screen




MINI SPOILER

During the objective "Keep up with Petrovich" you will come come across a mill. There is a small river that runs along side of the mill. At the base of the water wheel there is a spot for you to completely emerge yourself under water.

This achievement is fairly quick to get, but the trick is finding a suitable pool of water. If you can't seem to find any deep enough you can either try crouching or try a different level. With a little time, luck, and patience this little achievement can be yours.

Another great place to get this one is right at the beginning of the mission "Onward to Frankenau". I missed it in the other mission and didn't want to play it again.

When you come down the first hill there will be 5 bad guys. Kill them and take a right, there will be a pool right by a giant rock. Just stand near the rock and press in it. Hold and just sit the screen will eventually turn red and you got it.