The numbered PTs at Pearl were PT20 thru PT30 inclusive and PT 42.
I checked the map of ship dispositions at 0800 on 7DEC41 and notice that the SACRAMENTO was in a "nest" with four other craft at a hard dock in Southeast Loch.Simply put the attacking craft, particularly the torpedo planes, came directly over this point at an extremely low altitude on their run in to Battleship Row. Low trajectory gunfire from this point could well have hit the Hickam Field Contol tower, the Battleships themselves, any number of administrative buildings in the area and, if one was really unlucky, either of the two the fuel storage "farms" that bordered Hickam.
If it happens that your uncle was aboard the SACRAMENTO, and the CO or Gunnery Officer ordered them not to shoot, he most likely saved the lives of military personnel and civilians that would have been in his line of fire, or wounded/killed when the projectiles finally fell to earth.
A very difficult choice for an officer to make in the first minute of a war.