This cover has several things going for it (in addition to the lovely mint paper color):
- Crisp military insignia and name of the ship in the corner card
- Triangular officer KBC cachet with the HQ number
- It was sent between military KBC postal zones
While the postmark is illegible, the enclosed letter dates the usage as June 1974. The letter was sent from a naval officer to the Naval Medical Facility in Saigon at KBC 4595.
You can view more military covers with insignia on my website.