That's not how Boats work!

TBA"Place Cassie on an underwater map"

- BATTD description

 is a hidden achievement in Bloons Adventure Time TD. It is unlocked when placing down Captain Cassie or Commander Cassie in any one of the following maps: Underwater Junction, Chasm of the Deep, Underwater Mall, Fish Parliament, and Underwater Trench. It rewards one Uncommon wish orb upon completion.

Strategy
After unlocking Captain Cassie, make sure you have her in party and simply open up another game in Underwater Junction or Chasm of the Deep, then place her anywhere on the map.

Trivia
TBA