Hello and welcome, Omega.
Actually, both the 4th Fleet and the 4th Expeditionary Fleet has been lost.
The 4XF was decimated by Mishhus at Tami.
Wes, please refresh my memory on how the 4th Fleet met its end. I could remember several events that could've caused it, but we only lost the 4th once.
Anyway, it's been a long bloody war with the Mishhus. Yamatai has not lost a war yet, but it's had its share of beatings on the battlefield.
Nepleslia and Yamatai are currently on friendly terms. But the latter was an ex-colony of the former. And the former had been under the latter's political control for years, and seceded in the middle of a war. Diplomatic meetings are, shall we say, "awkward".
And yes, the courageous catgirls and humans of Yamatai are currently fighting the Mishhuvurthyar. The Mishhus are disgusting, slimey, many-tentacled monsters. With psionics. (A GM's dream, really.) They threw the first punch, so to speak, and the only diplomatic overtures from them so far has been calls for Yamatai to surrender.
I believe I'm cross-posting with Doshii. But our answers are not conflicting.