"Good job," Luke says, still sunk low in the water so he can be close to Jack. He reaches out to find one of Jack's hands, then gently shapes it so it's a little more cupped.

"Feel that?" he asks, gliding Jack's hand through the water slowly. "See how it feels like you're pushing the water away and then pulling it back toward you? All of this doesn't take much energy or effort once you're really good at it and that's very important in an emergency."

He lets go of Jack again to let him try on his own, watching the way his arms and legs move under the water. It's only the first step, but Jack is always so eager to learn, always filled with such desire to do more and Luke has no doubt he's going to take as well to swimming as he has everything else.

"If you're feeling brave, we can always try it without your jacket," he says. "I'll be right here for you to hold onto if you need."