What is the meter of the poem, "Dulce et Decorum"?
I will use the first stanza to demonstrate the poem's meter. Feet are separated by a vertical line, "|," and stressed syllables are in bold.
Bent dou | ble like | old beg | gars un | der sacks
Knock kneed | cou ghing | like hags | we cursed | through sludge
Till on | the haun | ting flares | we turned | our backs
And towards | our dis | tant rest | be gan | to trudge
Men marched | a sleep | Ma ny | had lost | their boots
But limped | on blood | shod All | went lame | all blind
Drunk with | fa tigue | deaf e | ven to | the hoots
Of gas | shells drop | ping soft | ly be hind
You can see that the first line is regular iambic pentameter. This means that it has five feet, each foot consisting of one unstressed (or unaccented) syllable followed by one stressed (or accented) syllable. This type of foot, with one unstressed syllable followed by one stressed, is called an iamb (this is where the adjective iambic comes from), and the word pentameter comes from the fact that there are five (penta-) feet per line.
However, things get a little trickier after that first line. The second line seems to begin with two feet which do not follow the iambic pattern. They are called trochees, and a trochee has one stressed syllable followed by one unstressed. Often, trochees can sound more aggressive than iambs because the accent comes first rather than second in the foot, and it makes sense here that the poet would want to draw our attention to the terrible sounds of the soldiers' knees knocking together and their raspy and guttural coughing. Lines 3 and 4 resume regular iambic pentameter.
In line 5, another trochee is substituted for the third foot, disrupting the meter after the word "asleep" as if to jolt us, readers, out of the lulling effect of a regular meter. This substitution also draws attention to the word "Many" as if to emphasize the number. Line 6 begins with an iamb, but then another type of foot called a spondee is substituted for the second and third feet. A spondee consists of two accented syllables, and it tends to disrupt the rhythm, as they do here. Five accented syllables in a row slows down the pace of the line, and it is, I'm sure, no mistake that this occurs as the speaker is describing the soldiers limping, slowly and painfully. The rhythm here, in the two spondees, also becomes plodding and slow.
The next line begins with a trochee before resolving into the more regular iambs, and the final line of this stanza starts with three iambs, nice and regular, but then ends with an anapest, another kind of foot that consists of two unstressed syllables followed by one stressed. These two unstressed syllables occur just as the speaker describes the "soft" sound of gas shells dropping far away, and so the repetition of unstressed sounds seems almost to mimic the sounds they describe.
Ultimately, most of the lines in the poem are written in iambic pentameter (even though there are many substitutions, like the ones I've described). Clearly Owen uses accents to great effect, to draw our attention to certain words or descriptions and even to mimic their sounds.
The poem's meter is primarily iambic pentameter, which is the style Shakespeare used for his plays. In iambic pentameter, each line has 10 syllables. The syllables alternate in an unstressed/stressed pattern, beginning with the unstressed syllable. For instance, this line
Till on the haunting flares we turned our backs.
would look like this if we wrote it to show the meter:
Till on/ the haun/ ting flares/ we turned/ our backs.
However, sometimes Owen deviates from this metrical pattern, as in these lines, which have 11 syllables each:
“GAS! Gas! Quick, boys!-- An ecstasy of fumbling,”
“As under a green sea, I saw him drowning.”
Perhaps Owen uses this break in the pattern to emphasize that war is not "sweet and fitting."