The other term I repeatedly heard soldiers and Marines in Vietnam use was the word “gook” to refer to the Vietnamese. The term’s origin goes back to the Korean War.
The words in Korean, mi gook, mean “American.” They are derived from the Chinese mei guo (美國) which also show up in Vietnamese as Mỹ quốc. The first word in all three languages literally means “beautiful,” but it was used to mean “American” because of the similarity in sound to the letter “m” in “American.”
When Koreans came across Americans, they said “mi gook.” That is, “Americans.” The GIs thought they were referring to themselves, meaning “I’m a gook.” To Americans, who tend to think of themselves as superior, Asians, over time, were all the same. They were all gooks.
The way we Americans used “number one,” “number ten,” and “gook” in Vietnam reflects our own sense of our pre-eminence among nations. Our condescension toward Asian races does not reflect well on us.