Week 8, this will be used to teach you the basics for week 11 in the field, you will stay in the shacks. The 13 km rucksack march is also in week 8. Come week 11 the majority of everything you learned throughout your entire basic field related will be put to the test. You'll do two days in the biv and two days in the FOB. I loved the field. It was the best part of my entire basic. Worry about the weeks leading up to it and avoiding counselings and injuries, not the field itself.