Just when it seemed like Sam and Callen's situation could get any worse ... it does! Big time!

On NCIS: Los Angeles Season 6 Episode 1, the agents are stuck with two terrorists on a submarine that's been turned into a torpedo... and that's not even their biggest threat. Hetty ditches her call to Washington DC and returns to manage the crisis.

In the recently-released NCIS: Los Angeles Season 6 premiere promo, Callen gets the message out: "We are in the sub!"

That call may be the worst mistake he ever made, because the result is brutal. It's so bad that Hetty's only advice is to pray.

Watch the promo now to find out what makes Sam and Callen's situation even more life threatening than being on a submarine filled with Ammonium Nitrate.

For more on NCIS: Los Angeles Season 6 Episode 1, check out these "Deep Trouble, Part II" photos.