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As for the Navy results, this is what John said to me.
Basically the two blockades being cleared by Highgarden meant that most of the Greyjoy orders were unusable in their current form, and attempting to do most of what they wanted in the timescale led to their navy arriving at the Whispering Sound at virtually the same time yours did. Had I left the Highgarden navy at port, you would have been defeated, probably, and the end result would have been an assault on Highgarden, which probably would have failed but still done more damage than what transpired. Your intent was to join up with Highgarden, the Highgarden spies knew both navies where approaching at approx the same time and attempted to meet up with you. Rolls on all three admirals skill to determine what happened led to a strong Greyjoy advantage so they were able to meet both groups seperately and fight two battles as the larger force, rather than one as the smaller. The damage to your fleet and the Tyrells was relatively light, and you were actually in a strong position, with the new Tyrell shiips mext phase you would have smashed through the blockade.