Found this from the podcast on 3/26 I believe
Source: Official Lost Podcast transcript/March 26 - Lostpedia

Carlton Cuse: Did Locke really blow that submarine up?
Damon Lindelof: Well I would say that it certainly appeared that he, uh, that he blew it up. You know-
Carlton Cuse: Exactly.

I find it intresting that Cuse says APPEARED that he blew it up...

__________________
Please don't give up, Des. Because all we really need to survive is one person who truly loves us. And you have her. I will wait for
you. Always. I love you, Pen

DESMOND: I love you, Penny. I've always loved you. I'm so sorry. I love you!
PENNY: I love you too.
DESMOND: I don't know where I am, but--
PENNY: I'll find you, Des--
DESMOND: --I promise--
PENNY: --no matter what--
DESMOND: --I'll come back to you--
PENNY: --I won't give up--
BOTH: I promise. I love you.