"Naming of Parts" is a poem that relies heavily on apostrophe, featuring a speaker who addresses a group of soldiers to deliver a lesson about military-issued rifles. This, however, isn't apparent right away, since the first line doesn't necessarily clarify the setting of the poem or reveal who, exactly, the speaker is addressing. Rather, these details develop over the course of the poem, as the speaker uses words like "we" and "you" to make it clear that there are other people listening to this lecture. For instance, the following passage makes it obvious that the speaker's words are intended for an audience (and not just the readers):
... And this
Is the upper sling swivel, whose use you will see,
When you are given your slings. And this is the piling swivel,
Which in your case you have not got.
When the speaker suggests that the listeners will understand the use of the "upper sling swivel" when they receive their "slings," readers sense that the speaker is not talking to them, but rather to a specific group of soldiers. As if to further underline this idea, the speaker adds that the soldiers do not have "piling swivel[s]" on their rifles, ultimately bringing in more specific details that emphasize the fact that the readers are not the speaker's intended audience. After all, it's very unlikely that the readers are in a similar situation as the soldiers while reading the poem, since they're surely not holding rifles, nor are they expecting to receive straps to connect to sling swivels.
At the same time, the overall effect of apostrophe is interesting in that it actually does invite readers to step into the world of the poem. Indeed, readers will perhaps feel like they are standing alongside the other soldiers and listening to the boring rifle lecture, since the instructor keeps using "you," therefore inviting readers to step into the soldiers' perspectives.
As a result, the lapses in apostrophe at the end of each stanza become even more noticeable. That is, whenever the poem shifts from addressing the soldiers to focusing on nature, readers feel a sudden and abrupt change, and many readers attribute these lines to a daydreaming soldier. This interpretation makes sense because it's an easy way to make sense of an otherwise startling interruption of the instructor's lecture.
Regardless of whether these thoughts really belong to a distracted soldier, though, one thing is certain: the lines of this poem are characterized by whether they make use of apostrophe, since the rifle lesson depends upon this device but the observations about nature do not. In this way, apostrophe significantly contributes to how readers make sense of the poem.