DOS Games made for DOS require an emulator to run on Windows. Use DOSBox or a frontend like D-Fend Reloaded and read this guide to play DOS games on your Windows PC.
Irem has developed a number of sequels and related games, including R-Type II and Armed Police Unit Gallop. Their XMultiply, although not part of the series, has similar themes and gameplay, and was released around the same time as R-Type II. However, before any of these games was Katakis, a 1987 clone produced by Factor 5 for the Commodore 64 and the Amiga.
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