Taking full advantage of America's lingering ninja boom, the Ninja Gaiden arcade game was released four months earlier in the west than it was in Japan. This game is not to be confused with the much more well known NES/Famicom game by the same name though, and here's where things get a bit confusing! According to this wonderful interview with Hideo Yoshizawa and Keiji Yamagishi
by gaming.moe's Heidi Kemps, the two titles were in production at the same time, and retained the same names to achieve name recognition (seemingly at the insistence of the company president). The arcade game hit America quite awhile before the NES game did, but didn't hit Japan until after the Famicom version. Regardless, history has already determined which Ninja Gaiden people would end up caring about.