Answer: BELUGA PAL
Each answer has exactly one repeated letter. These letters can be used to spell TIC TAC TOE.
If you write each answer in a 3x3 box, the doubled letters almost form a winning tic-tac-toe combo.
For instance, in BAPTISTRY:
BAP TIS TRY
... the two Ts and the B form a three-in-a-row.
And in CITY GATES:
CIT YGA TES
...the two Ts and the G form a winning diagonal.
In each answer, the letter with the "winning move" occupies a different square. Order them by which square is used to complete the row:
BEL UGA PAL
In a show of cetacean unity, the playful dolphins have recruited a friendly BELUGA PAL to help guide your sub!