1. open the editor
2. place a diver at the beach
3. play as the diver and before entering the water, just switch to you pistol
4. as long as you are in the water, you are not able to switch to your weapon
or
3. play as the diver and while swimming or diving, press the
"switch gun / handgun" key (; by default) and you won't be
able to shoot your SDAR as long as you are swimming and diving.