One of my navy friends told me this joke to make me laug(i was a bit down at that time he told me it). Its probably old..but very funny :
Response from a junior (very junior) sonar watchstander
"Sonar - Conn, Report all contacts in preparation in coming to periscope depth"
"Conn - Sonar, I hold no contacts - how 'bout you..?"
"Sonar - Conn, Supervisor to the Conn"
And this one :
Submarines are safer than airplanes. Proof in the fact is there are more airplanes in the water than submarines in the air!