Dolphin Intelligence: 3 Early Dolphin Experiments Funded by the U.S. Navy (2006)

Dolphins were used by the Navy to find explosives (and perhaps detonate them) [1], to identify and warn about submarines, and other related efforts. So, getting a good guage on their intelligence was a priority for the Navy.

Also, just making sure that the dolphins weren't really aliens that were going to abandon us to make room for a superhighway[2].

EDIT: For all the young whippersnappers not getting the reference, that series has left many traces on American culture (and video games), it is not just "another book". Let us old fogies reminiscence ;)

[1]: https://www.diversinstitute.edu/bomb-sniffing-dolphins-navy-...

[2]:https://en.wikipedia.org/wiki/So_Long,_and_Thanks_for_All_th...

There have been two interesting studies that further support the hypothesis of somewhat complex communication system. One was done in Florida with wild dolphins who hunt cooperatively. One dolphin drives the fish,while others act as a barrier. Such cooperation requires sophisticated acoustic communication. Another study was an experiment with dolphins in managed care. Dolphins were asked to push two separate buttons at the same time, but they could not see each other. So they had to communicate acoustically to achieve the perfect timing and push the buttons together.

I seem to recall a time when they all left earth and thanked us for all the fish...

They were trying to teach them to communicate at Epcot in the mid ‘90s.