How do I retrain navies?

[Ginger]

"Appropriate port" as in, it has to be a port (there are 3 levels) that can build that type of ship in the first place. i.e., don't expect to retrain a trireme in a level-one port (dockyard?). Took me awhile to realize this.

Im pretty sure that is the case, but ive never actually checked for certain as I tend to under-use navies. I rarely bother building anything beyond triremes

[The Stranger]

you can only retrain a unit if the unit is avaible in the recruitment queu