Back in the 1980’s, Atarisoft were doing official conversions for the Commodore 64. Vanguard was one of them!
We learn of this conversion thanks to Mat Allen who has documented the conversion briefly in Digital Press. We hope to learn more about the conversion soon as a result.
We are not sure at present how far the game got, or why it was cancelled, but we are guessing it was due to Atarisoft breaking up at somepoint.
At present we have no credits or anything for the game, so its very early days along with another bunch of Atarisoft games we have added entries for.
Do you know more?
(Additional source credits – Mat Allen)