Owen began The Sentry while he was receiving hospital treatment at Craiglockhart in 1917. He made further alterations at Scarborough in 1918, when he was training to return to France. The Sentry was finally completed in France in September 1918, a few weeks before his death.
The sentry was a very personal poem, therefore, the eighteen month gap between the experience and its translation into words suggesting an experience of great intensity.

The setting is an old Boche dug-out’ which a party of English troops has taken, but not without being seen: consequently, it comes under enemy fire, ‘shell on frantic shell’ pounding its position. The co-opted dug-out is a ‘hell’ on earth, not only because of the artillery bombardment, but also because of the bad weather. It is raining heavily: into the dug-out pour ‘waterfalls of slime’ with the result that the men stand in ‘slush waist-high’ and cannot climb out. The first line “We'd found an old Boche dug-out, and he knew,” owen uses “he” as a derogatory term for all the soldiers of the opposition. This line is also an enjambment as the first line and its thought continues to the next line.

The second and third line describe the “shells” or bombs “And gave us hell, for shell on frantic shell Hammered on top, but never quite burst through” – here owen describes how the shells never penetrated into the place they were, but the shells were close. He also uses a figure of speech, namely personification, to describe the shells as frantic.
The words “hell” and shell” in the second line have an internal rhyming. And the repition of the word shell tells the readers that the bombing was one after the other.

The next to lines tells the readers how the bad weather adds on to the soldiers misery, how even nature was not on their side now.
“waterfall made of slime” is an oxymoron because as a reader we would most likely think of waterfall as pure and clear.

The seventh and eight line “What murk of air remained stank old, and sour
With fumes of whizz-bangs, and the smell of men” Owen adapts Lady Macbeth’s adjective (‘Hell is murky’) to his purpose; the dug-out is a hell-hole, not only because they cannot see through the smoke of the whizz-bangs, but also because of its olfactory sensations. It ‘stank old’; this combination of an Anglo-Saxon past tense and an adjectival adverb conveys the rank odour with a monosyllabic force.
In the line “Choked up the steps too thick with clay to climb.” Owen has used alliteration.

The verse is basically iambic but trochees at significant points disturb the rhythm and effectively accentuate the unrest and tension, while the break at line 10 suggests that Owen is looking for his readers to pause and maybe gasp.

“If not their corpses. . . .” here owen ends the sentence with three full stops, this is a paralinguistic feature which conveys that no more can be said, its too sad. And lot is left unsaid.

Finally, one of the whizz-bangs hits its target, leaving them gasping for even a ‘sour’ breath of air. What happens next Owen records by means of onomatopoeic verbs. He accompanies the sentry’s entrance into the dug-out with a sequence of u-sounds: ‘thud! flump! thud!’. Down ‘the steep steps’ into their trench, he is said to come ‘thumping’ rather than merely falling or tumbling – so powerful and debilitating was the blast that blew him off his feet and into ‘hell’.
Owen narrates this episode in rhymed iambic pentameter

Owen then descripes how the injured sentry “whines”- this word shows the helplessness of the almost blined sentry.
Owen meets the demands of rhyme and metre by a skilful combination of direct speech, indirect speech and plain description. In the line “"O sir, my eyes — I'm blind — I'm blind, I'm blind!"” The politeness with which the blinded sentry addresses his commanding officer (‘O sir’) stands in ironic juxtaposition to his repeated realisation that he has lost his sight, thereby inspiring a deep pity for him.

Owen uses very detailed nd gruesome imagery in the line “Eyeballs, huge-bulged like squids” here not only does owen create a haunting image but he also uses personification.
The following line “Watch my dreams still;” tells the reader what a traumatize image that was that is still clear and vivid in owens mind.
"Yet I forget him there." Is the next line where owen agrees to have left the sentry with someone else to continue his duty in war.

Owen uses personification again in the last line of this stanza to describe the air as shreaking

The line “And one who would have drowned himself for good.
Here is double ambiguity, as to the identity of "one" and "for good" as a final act simply, or as leading to some better existence;

I try not to remember these things now
- conveys the calm that comes from his selective amnesia; the steady rhythm of the line suggests that he has regained his composure. Respite, however, is only temporary. The blinded and shell-shocked sentry has the last ‘word’. His ‘moans and jumps’ - not to mention ‘the wild chattering’ of his teeth - resurface in Owen’s consciousness and reclaim his attention:

combined visual-aural image, "And the wild chattering of his shivered teeth" is horrifying and unforgettable. Alliteration is also used here, on letters such as ‘t’ when he describes “the wild chattering of his broken teeth” giving a broken sound to the sentence, mirroring the broken fragmentation of the soldiers lives as they fight for their country

The poem ends with the almost blind sentry saying “I see your lights” this could be a almost death incident.