If the US passport holders want to apply visa at Vietnam Embassy, they should to know that:
Visa administrative Institution: Vietnam Embassy
Processing time: depends on you how fast you need. But for sure, you should make a call to Vietnam Embassy for details.
Required Documents: passport, money and 1 new envelope with stamp on it and your exact home address in order to avoid losing issues.
How to apply: please take a look at contact information of Vietnam Embassy below
EMBASSY OF VIETNAM IN WASHINGTON
Address: 1233 20th Street N.W, Suite 400, Washington D.C.20036
Fax: +001-202-8610917 | 8611297
Email: firstname.lastname@example.org | email@example.com
Website: www.vietnamembassy.us | www.vietnam-ustrade.org
CONSULATE GENERAL OF VIETNAM IN HOUSTON-TEXAS
Address: 5251 Westheimer Road, Suite 1100, Houston, Texas 77056
Phone: +001-713.850.1233 | 7138771326 | 7138400096
Fax: +001-713.871.0312 | 7138100159
CONSULATE GENERAL OF VIETNAM IN SAN FRANCISCO
Address: 1700 California Street, Suite 580, San Francisco, CA 94109