Lines 1-8 Summary

Line 1

It seemed that out of the battle I escaped

• This sounds like the start of a pretty good day. No one really wants to be trapped in battle. Looks like our speaker may have found a way out. 
• Though it seems like our speaker is in the clear, it might be a good idea to pay attention to that very word, because, well, things aren't always as they seem. The word "seem" sort of makes you think of a dream, or some other unreality. 
• Because we're so early in the poem, it's good to look out for any clues that might help orient you as you go along. The fact that the speaker has escaped from battle is probably a good hint that this poem will have something to do with war. (As if "Wilfred Owen" on the title card didn't tip you off already.)

Lines 2-3

Down some profound dull tunnel, long since scooped
Through granites which Titanic wars had groined.

• We know from the first line that the speaker seems to be away from battle. It looks now like he's fallen down a tunnel. This is a little strange, and maybe not the beginning of the best day ever.
• Owen describes the tunnel as dull, which is never really a good thing. Have you ever been stuck talking to someone dull at a party? Or had a dull headache? No fun. 
• He also describes the tunnel as profound. Vocab alert: Profound has two meanings. One means physically very deep—so that makes sense in this case—the tunnel could be buried very deeply. The other meaning is very intense or deep in an emotional sense (that's the one you're likely familiar with). This definition doesn't really apply yet, but let's keep it in our back pockets in case it does further into the poem. 
• "[L]ong since scooped / Through granites which Titanic wars had groined" is quite a mouthful, but he's basically saying this tunnel has been carved out of the hard stone (granite) that huge wars have created. If you're having a tough time picturing how wars can create tunnels, just remember that in World War I (when this poem takes place) there was tons of fighting in trenches—or tunnels—that the armies dug as protection, and as a sneaky place from which to fire at their enemies. 
• The Titanic wasn't just a movie with Leo DiCaprio at his cutest (but it was that, too). The Titanic was an actual real live ship that was huge, and sunk (pretty famously) in 1912, just a few years before Owen wrote this poem. Comparing the magnitude of the wars to the ship shows the incident was fresh in his mind.

Lines 4-5

Yet also there encumbered sleepers groaned,
Too fast in thought or death to be bestirred

• In the tunnel there are people. Groaning and sleeping. The creep factor just went up a notch. 
• Not only are people groaning in their sleep (why are they groaning—from pain?), but Owen says they're too busy either thinking or uhhh, being dead, to notice him at all. 
• This is looking suspiciously like a Walking Dead episode and not at all like a welcome alternative to battle. We're officially weirded out.
• You might start to notice a rhyme scheme unfolding, too. Owen is writing in rhymed couplets, so the last words of the first two lines rhyme.. Well kind of of. See, Owen uses slant rhyme so the rhymes don't sound all harsh and clangy. He likes his rhymes subtle. The rhyme scheme works to kind of build tension—like creepy music in a horror movie. We don't know what's coming next, but the rhythm these rhymes create ups the feeling of anticipation. You might start to form a pit in your stomach. 

Lines 6-8

Then, as I probed them, one sprang up, and stared
With piteous recognition in fixed eyes,
Lifting distressful hands as if to bless.

• Not sure why on earth this guy would want to probe these miserable groaning (and possibly dead) people, but, hey, who are we to judge? It's unclear whether the speaker is actually probing them with something—like poking them with his hand or a stick—or if Owen means the speaker is probing them with his eyes. It could be either. 
• Okay, so our speaker is poking around and one of them springs up. Um, run for your life?
• So one of these sleepy and/or dead guys looks at our speaker with what Owen describes as "piteous recognition." Piteous just means that they make whoever he's looking at feel bad for him. The recognition part is strange. Maybe this person knows the speaker from somewhere. 
• He's staring at our speaker, looking pretty pathetic, and he's lifting his hands up in distress—or extreme anxiety, sorrow, and pain—which isn't that surprising considering the state of these people, but it's a little odd that he's lifting his hands as if to bless our speaker. 
• By now you might have noticed that all these lines are somewhere around the same length—and most of 'em have about ten syllables. If you're thinking iambic pentameter, you're not wrong. But get ready for some metrical weirdness, because these lines are nowhere near regular. For more on this, check out "Form and Meter."