CHAPTER 1: INTRODUCTION TO LINE OF DUTY (LOD), 1.1 What Is a Line of Duty Determination? A Line of Duty (LOD) determination is an official administrative investigation conducted by the military to decide whether a service member's injury, illness, or death occurred IN the line of duty during qualifying military service. This determination is not simply a bureaucratic checkbox — it is the gateway to critical medical benefits, disability processing, and compensation for service members and their families.