One of the poem's most prominent features is the speaker's use of alliteration, which appears in almost every line. The alliterative moments become particularly prominent when the intensity of the speaker's words increases.
At first, the speaker uses alliteration consistently but somewhat sparingly, repeating roughly one alliterative sound per line. For instance, lines 2 through 4 ("love you land ... come and go") each contain one alliterative repetition; line 2 features the /l/ sound, line 3 features the sibilant /s/ sound, and line 4 features the /k/ sound:
love you land of the pilgrims' and so forth oh
say can you see by the dawn's early my
country 'tis of centuries come and go
Using alliteration, the speaker connects and emphasizes important words, especially in line 2, which spotlights the words "love" and "land." In this way, alliteration helps the speaker underline words that exaggerate the poem's intensely patriotic tone.
In other moments, the speaker's use of alliteration creates a feeling of intensity that reflects the speaker's passion (regardless of whether this passion is actually sincere). For example, lines 9 through 11 ("why talk of ... the roaring slaughter") are particularly alliterative, repeating the /w/, /b/, /th/, /h/, /r/, and /l/ sounds:
why talk of beauty what could be more beaut-
iful than these heroic happy dead
who rushed like lions to the roaring slaughter
By infusing each line with so much alliteration, the speaker ties certain words to each other while also creating a fairly arresting overall sound that aligns with the subject at hand. Indeed, the speaker describes soldiers rushing to their death in battle, so it makes sense that these lines sound particularly intense. In keeping with this, alliteration helps the speaker set forth the kind of tone that an impassioned American patriot would most likely use when talking about war and the country.