S-ranking Extra Ops 83. You can do it by clearing it under 16 minutes. The trick is to do it fast and make sure to Fulton out most (if not all) of the enemies and do not kill anyone (if an enemy tank runs over anyone by accident, it won't count). It's easier to get an S-rank if you do not let the guards spot Snake until the commander pops out at the very end. Use the Mosin-Nagant to knock him out. I used a lot of up-levelled/improved smoke grenades and even colored smoke grenades so enemies didn't see me when I used the Fulton launcher on the troops. I also placed some Fulton mines next to them when they were blinded by the smoke to automatically get rid of them.

Make sure to equip the Sneaking Suit, Night Vision Goggles, and throw the smoke grenades at your feet so that nobody sees you when you use the Fulton launcher. I managed to hide in the empty warehouse building so make sure you have the Stealth Mat to hide yourself when the troops come running towards you and look inside. Oh, and you can get the battle suit with the helmet from S++ Outer Ops missions, because that's where I got mine.