Give her the ring (assuming you can afford to)...

Get engaged...



When she bails from the Navy, tell her about the pre-nup that your lawyers drew up...



She'll either marry you under the conditions you (both) put forth, or she'll prove she wasn't worth it by bailing on you...

Then get the ring back...
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So save me your sorries, I'm raising an army...

Fortes Fortuna Adiuvat.