The first I’d ever seen at all?

considers

Probably some extremely-poorly-dubbed TV release long prior to anime gaining mainstream popularity in the US, as there were a couple series that people brought in on shoestring budgets. Speed Racer, maybe. That was in the US on TV reruns ages ago.

Speed Racer, also known as Mach GoGoGo (Japanese: マッハGoGoGo, Hepburn: Mahha GōGōGō), is a Japanese anime television series produced by Tatsunoko Production, that aired on Fuji Television from April 1967 to March 1968. In the United States, the show aired in syndication at approximately the same time.

For American consumption, major editing and dubbing efforts were undertaken by producer Peter Fernandez, who likewise not only wrote and directed the English-language dialogue but also provided the voices of many of the characters, most notably Racer X and Speed Racer himself.

www.youtube.com/watch?v=gHn6KCvRsdI