Civilization 5 Elizabeth-specific achievement domain?
Solution 1:
After having a look at both rules and source code, I can conclude that embarked units are NOT considered naval units.
When a land unit is embarked it is unable to attack and unable to defend itself against any attacks. Any naval unit can destroy an embarked unit and will not even lose its remaining moves while doing so. Cities and ranged units can also easily destroy embarked land units by bombing them. In effect, embarked land units are considered to be non-military units.
Also, wonders and abilities given to naval units will not be applied to embarked units, and I have killed well over 350 embarked units with Elizabeth (love doing that) without getting this achievement.