Hostile Shield Secured Achievement
Hostile Shield Secured10
Snuck up & stole the shield from a Shielded Infantryman
You will encounter your first Shielded Infantryman at the end of "Special Missions HQ" mission. A short cutscene will begin when you enter a large room and he will appear alongside three soldiers. Take out the other enemies first so only the Shielded Infantryman remains. Sneak up behind him to take him out with hand-to-hand combat or your weapon. When he drops his shield, pick it up and the achievement is yours.
Alternatively, you can obtain this in Kobin's first COOP mission, Opium Farm. If you follow the left side of the map from the beginning, you will come to an open garage with a Shielded Infantryman looking out into a courtyard. Sneak up behind him, knock him out, then pick up his shield.