This cover contains a letter to the Mayor of Saigon from the Commanding Officer of the Navy Shipyard. "Hai Quan Cong Xuong" was the main shipyard by the Saigon River not far from the South Vietnamese Naval Headquarters.
The shipyard was a large complex with several departments responsible for maintenance and repair.
"Cong Van" handstamped at the top of the cover means "Official Document". Written beneath the handstamp is, "001/HQCX/HC/QT" where "001" is presumably a document number, "HQCX" is the abbreviation for Hai Quan Cong Xuong - the Naval Shipyard, 'HC" is not known - perhaps a department abbreviation, and finally, "QT" for Quan Thu, or military mail.
As the cover is unaddressed, it most likely was included in a larger envelope (think interoffice mail) or hand delivered.
In the enclosed memo, Naval Commander Tran Van Chon requests the official price of firewood (coal?) for February 1958 from the Mayoral office. This information was needed for his accounting department in their compilation of the monthly budget.
The request was signed by Navy Lieutentant Tran Van Bieu, Executive Officer of the Naval Accounting Department.
Tran Van Chon went on to become the Secretary of the Navy, a position he held up to the last days of the war. He refused to be evacuated and was imprisoned a number of years until Admiral Emo Zumwalt and other senior retired officers petitioned for this release and immigration to the U.S. Apparently, Chon and Zumwalt had formed a strong relationship during the war. They were reunited for a few years before Admiral Zumwalt passed away. Admiral Chon is nearing 80 years old.
Thanks for Vinh Nguyen for his assistance with this cover.