Short answers, pulled from the story.
Killed in action describes deaths caused by enemy or hostile forces at the moment of action. This classification applies to front-line combat troops as well as naval, air, and support forces without requiring a soldier to fire a weapon.
John Kipling died unidentified among thousands of soldiers killed in World War I. His father Rudyard Kipling wrote an inscription for his son's grave at the Thiepval Memorial after governments struggled to identify fallen soldiers without modern technology.
Families wait years for confirmation that a loved one is gone when search efforts fail over time. Personnel lost in deep water or rough seas transition from missing in action to presumed killed in action once no evidence of survival emerges despite extensive searches.
The distinction separates immediate battlefield death from later mortality after medical evacuation. Medical staff track these cases differently than those who fall instantly because it affects how families are notified and how records are kept.
A soldier hit by their own side's weapons still receives the killed in action classification if engaged with enemy forces. The definition focuses on deaths caused by hostile attacks rather than internal accidents like accidental vehicle crashes or murder.