The May 22 edition has an article abut the ceremony at Memorial Plaza. Among other things it says that there will be a 21-gun salute by the Whiting Field Color Guard. I suspect what is meant is there will be three rifle volleys fired by a squad of riflemen from Whiting Field.
A 21-gun salute is usually fired by cannon or ships guns to honor presidents, kings or other countries for example. There maybe lesser number of guns for lesser lights.