This isn't required to complete the game, but once you get to the torpedo in the sub rotate it so you can enter it on the back side of it. You will have 3 stages to pass without missing a shot or bad guy. Also, shooting a lady pop up in stage 3 counts against you.
Credit goes to Tassie Tiger:
Stages 1 and 2: Don't require speed, just hit the correct targets.
Stage 1: Hit targets in correct order.
Stage 2: Hit targets in any order.
Stage 3: Requires quick reflexes and memorizing the order and position of each target.
(1) Shoot the guy 2nd from right
(2) Guy with the card in his pocket
(3) Piano player
(4) Girl on the right
(5) Animal skull
Stage 2: (in no particular order)
(1) Shoot the guy wearing mexican hat
(2) Square sign to the right of the deer head
(3) Light fitting on the left
(4) Bald barman
(5) Guy with the card in his pocket
Shoot all baddies without missing one or hitting innocents
For the 3rd Stage you need to learn where each baddie is going to pop up and be in position to shoot them.
For more than 2 baddies, have sights over to left before they pop up then sweep to right hitting each baddie.