Caravel and Galleon requirements?

[Bobolopolous]

All the documentation points to no prereq's to get the Caravel or Galleon, and yet I can go a long time before they start showing up as possible units for build. What am I missing here?!

 

[eccentricity]

naval transports requirements are as follows:

galley:mapmaking; caravel:astronomy; galleon:magnetism; transport:combustion,oil; carrier:mass production,oil