... so it's in USNAINST 1530.1G 20Mar2023:
paragraph 6g. Foreign Exchange Cruise.
paragraph 7b. (2) (c). International Program Office: Language, Regional Experience, and Culture (LREC), Language Study Abroad Program, Foreign Exchange, and Tall Ship Cruises.
Just talking from DS, he's opting for 2/C summer cruise in Pearl Harbor and 1/C Foreign Exchange.