I have seen various Hollywood movies depicting both the surfacing and diving of a submarine. There is a certain "protocal" as far as the announcement and the sounding of the alarm horn.
When diving; the word "DIVE, DIVE" (spoken twice) is passed over the general announcement sytem with THREE blast of the diving horn.
Of course when surfacing, the word is passed three times; "SURFACE,SURFACE, SURFACE" with two blasts of the alarm horn.
... just trivia.... and something to post.