The second US embassy in Saigon was at No. 4 Thong Nhat, now called Le Duan. 

Postcard Photo of US Embassy at 39 Ham Nghi

My Uncle Ed Sanborn took the photo above in 1969 or 1970. While the embassy building is now gone, the US Consulate General is at the same location as the embassy's former consular section to the left in the photo. Now, on every day the consulate is open for business, there is a line of people outside on the sidewalk waiting to get a US visa.

The first American embassy was located at No. 39 Ham Nghi. It opened as a "US Legation" in 1950, becoming an embassy when the US formally recognized the Ngo Dinh Diem government in 1955. The building was the site of a bomb attack in 1965. 

The diplomats moved to the newly opened Thong Nhut location in 1967. The old embassy on Ham Nghi is now a bank.