When a grenade explodes, it's best to dive into deep water, as the resistance of the water can negate the force of the blast.
However, Glenn Hutchinson purposely dived deeper, and it was not just for this reason.
As a frogman, Flossie Wright couldn't possibly be unaware of this fact, so after deploying the grenade, she would definitely head quickly into the deeper water, and surely the direction would be straight ahead.
At the same time—
Flossie Wright was making her way toward the surface.
As a master of free diving, Flossie Wright nearly tapped into the full potential of her body, grabbing a bit of air immediately after releasing the grenade, then submerged into the deep water to wait for the blast to subside.
To avoid being discovered by Glenn Hutchinson and his team, she did not stay long in deep water, and quickly swam upwards.
But—
She underestimated Glenn Hutchinson's understanding of her.