What we've got here, gang, is a sonnet. And that means a few things as far as form and meter are concerned. Let's start with the overall form of the poem, shall we? We shall. So check it out: like any sonnet, "The Soldier" has 14 lines. Now, most sonnets are subdivided into two groups: the first eight lines (called the octave) and the last six lines (the sestet). In general, the octave introduces a problem which is then resolved in the sestet. What's more, the ninth line of a sonnet (i.e., the first line of the sestet) is called the "turn" or "volta" because this is where the poem usually starts to shift gears.
In the case of the "The Soldier," for example, the first 8 lines of the poem discuss the possibility of the soldier dying and reflect on the role England has played in his development. In the ninth line, the speaker imagines what it will be like in heaven (hint: like, totally super-awesome), and thus shifts or "turns" the direction of the poem away from the earth and toward an afterlife in the sky.
So that's how the poem is organized in terms of general structure, but how about line for line? Well, just like the good sonnet that it is, "The Soldier" is written in a metrical form called iambic pentameter. If that sounds familiar to you, that's probably because it's the most common meter in English poetry. If you've read any Shakespeare, you've run into this rhythm a time or two, even if you weren't aware of it at the time.
So what does iambic pentameter even mean? You see, every line of iambic pentameter contains five (pent- is the prefix that means five) iambs. Now, an iamb is a two-syllable pair that consists of an unstressed syllable followed by a stressed syllable. (Said out loud it sounds like this: da-DUM. "Allow," for example, is an iamb.) Not satisfied? You want an example? Well, okay then! Just peep line 9:
And think, this heart, all evil shed away.
Now, not every line in the poem scans as perfectly as this one does (what would be the fun in that?). Take line 8 as an example:
Washed by the rivers, blest by suns of home.
You'll notice that this line begins with a stressed syllable, rather than an unstressed syllable. (In the poetry biz, a syllable pair that contains a stressed syllable followed by an unstressed syllable is called a trochee.) It sure seems like the speaker really wants to emphasize that word "washed," doesn't it? Small substitutions like this are fairly common in poetry, so just be on the lookout for any metrical oddities. Any time a pattern is established, then broken, those breaks are designed to catch a reader's eye for emphasis (or catch their ear, as in this case).
But why use a sonnet to begin with? Brooke has his choice of any form of poem—or no form, even—but he went with this set-up. We think, though, that a sonnet is just a peachy choice. After all, the poem is celebrating patriotism and English-ness, and there aren't too many other forms of poetry more closely associated with England than the sonnet. And yet… this poem isn't exactly, 100% in the English style.
Let's roll it back for second. There are in fact many different types of sonnets, but the two most common are the Petrarchan sonnet (named after the famous Italian sonneteer Francesco Petrarca) and the Shakespearean (or English) sonnet. The major difference between these two types is the rhyme scheme. The octave of a Petrarchan sonnet generally follows this form: ABBAABBA, where each letter represents one particular end rhyme for that line. In this case, line 1 (A) would rhyme with lines 4, 5, and 8, while the sestet could take several forms (CDECDE and CDCDCD being the most popular).
The English sonnet, in contrast, has a rhyme scheme of ABABCDCD EFEFGG (the final two, rhyming lines are known as a heroic couplet, bee-tee-dubs). Now, we're telling you all this stuff about rhymes because Brooke's poem combines elements of both the Petrarchan and the Shakespearean sonnet. The octave is like an English sonnet, and its rhyme scheme is ABABCDCD. The sestet, however, takes the form of a Petrarchan sonnet and has a rhyme scheme of EFGEFG.
So now for the big question: why did Brooke use two different types of sonnet in the poem—one historically associated with England, and one with Italy? It may have something to do with the politics of the looming war, we think. It's not that England and Italy were fighting yet (that didn't happen really until World War II). But England was about to enter a conflict that began (and would be fought) on the European continent. In joining these two sonnet forms together, then, Brooke's poem is in a way enacting the kind of English-European fusion that was to come (only through arms this time, not words).