Before WW2 the term "Jap" was simply used as a shortening of "Japanese". Then during the War it became a derogatory term for Japanese Americans, who suffered from internment and other forms of racism.
After the war, how was the use of the term attacked and removed from discourse? Was there a movement against it similar to removing the term "nigger"?
Out of curiosity I ran "Hun" and "Jap" through the Google Ngrams viewer, and got this result. That is a really impressive spike on "Jap." It is even more impressive when you run other racial epithets through the site.
What does this mean? I don't think anybody thinks "Jap" was more common a phrase in the US language than the n-word. But was it more normalized, and thus more readily printable (and thus available for Google to index)? That's one quick theory.
Anyway, the curve shows that the term is insignificantly used up until 1941, rises in usage by 10X in 1943, then steadily falls until around 1947 when it hits more or less a baseline that is maybe twice of what it was prior to the war, trending towards a declining usage. I would like to say "this is, perhaps, what we would expect" but I'm not sure it is — I think if you had asked me ahead of time, I would have guessed that it would have risen and fallen with the war, and that maybe it would have still been used somewhat for the first 10-15 years after the war, then maybe an abrupt drop in the 1970s when people started to get much more concerned about the terms they used. So the fact that it is just a standard "long tail" distribution is kind of surprising to me. But I am no linguist.