On the main menu select Skirmish
Change your Home town/Civilization to Ottomans (Istanbul) (The flag Icon next to your gamertag)
Select Deck Builder -> Beginner
On row III remove one of the icons by clicking on it
Select III: Fortress Age
Select the 3 Galleys card to place it in your deck. (First card on the 3rd row)
Click Save and then back
Change starting age to Post-Imperial Age
Change map to Amazonia
Start the game and enter the cheat code: Nova & Orion
Select the flag icon in the bottom right corner of the screen (next to the mini map)
Choose the Beginner Deck
On line III Select the 3 Galleys option
This will deliver 3 Galleys to your Sea rally point and will pop the achievement.
Enter cheat code speed always wins to speed this up a bit.
Note: This has to be done using the 3 Galleys card, not a combination of cards - even if they give you more.