Official sources here today was the truck was on way to Guwahati from 4th Battalion of NAP situated at Thizama under Kohima district.
The retired havildar, identified as Yambemo Ngullie, was going to Dimapur for some work.
When the vehicle was proceeding towards Dimapur in high speed, it hit a big boulder lying on of NH 29 and turned turtle killing Yambemo on the spot and injuring other four occupants.
All the injured were admitted to various hospitals.
Police registered a case and investigation was on to ascertain the cause of the accident, sources added.