Hooray!
I always thought the AI would never launch naval invasions in RTW 1.5, but my current Aedui campaign has shown me that it's possible:
The Koinon Hellenon has shipped a full stack around the lands of my epeirote allies to besiege me at Dalminion AND the Ptolemaioi have captured Rhodos from the KH after being reduced to Salamis by the Seleucids. Now they are trying to invade Asia Minor. I have seen them besiege Rhodos one time in another campaign, but thought it might be coincidence.
Really a surprising thing, I have never been attacked by sea before.