The implication here is that some very highly advanced craft have indeed left our solar system, maybe as far back as 30+ years ago.
(Linda Howe has reported several times that there are three large craft that have left the solar system, all engaged in exploration: the USS Curtis LeMay, the USS Hoyt Vandenberg, and the USS Roscoe Hillenkoetter. I'm doubtful if this can be entirely trusted, but it's nevertheless pretty interesting. And yes, a Secret Space Program definitely exists, though its full scope is less well known.)
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