What is line of departure?
line of departure meaning in Military terminology / glossary / dictionary is:
1. In land warfare, a line designated to coordinate the departure of attack elements. Also called LD.
Source: JP 3-31
2. In amphibious operations, a suitably marked offshore coordinating line, which is located at the seaward end of a boat lane, to assist in the landing of landing craft and amphibious vehicles on designated beaches at the scheduled times. Also called LOD.
Source: JP 3-02