I am going to be the lone dissenter here.
This is an antiquated and IMO, inhumane method of punishment.
Its a bit of work to teach "Leave it" or "drop it" but these commands are much more valuable than humiliating a dog for tearing up underwear that he has access to and he sees nothing wrong with (remember, he doesn't speak human)
First off, I would put my underwear elsewhere (if he can get into your drawers..) so that he is no longer tempted.
This is the most simple way of solving this problem.
Then begin teaching
"leave it" and "drop it". I don't know when he is chewing them up but obviously if he is out of your sight for a few minutes, he is probably getting into trouble. So, watch him vigilantly for awhile until he has the above two commands down.
You can teach "leave it" with his kibble or any really great treat he loves (only use this treat when you are training). Put his lead on him and put the treat on the floor. Put him into a sit and make him aware of the treat. When he goes for the treat, give an "AH!" correction immediately and put him back into a sit. At first, give him the treat automatically when he goes back into the sit (even better if he looks at you).
Keep doing this gradually but for longer periods of time. Ie, have him sit, have him down, and if he goes for the treat, give the correction. Reposition him again. He will soon learn that when he looks away from the treat or doesn't go for the treat, he will get the treat. When he has this down, start using other articles and items like his toys, the kids toys, whatever. Then use your underwear. Drill him on this a few times a day to review.
You can teach "Drop it" pretty much the same but in this case, you would give him a toy, for example, play for a bit...Then give command "DROP IT" (but when you begin, have a treat in hand and make sure he can see it!). Give him the treat as SOON AS that thing drops out of his mouth. Continue this way until he is dropping the item on a dime and listening each time.
Soon, the treats can become random and intermittent. Ie, treat him every 3rd time (this actually creates more of a serious training response than treating each time).
I train "leave it" or "drop it" when doing other training drills too (keep training drills fun and varied, especially if he's a smart dog). Don't let him get bored.
Hopefully that works for you and for him in a positive and fun way.