The poem uses a great deal of alliteration, both for its musical qualities and for dramatic emphasis. Take the first three lines, for example:
Blow out, you bugles, over the rich Dead!
There’s none of these so lonely and poor of old,
But, dying, has made us rarer gifts than gold.
The emphatic /b/ alliteration in line 1 mimics the sharp, startling call of the "bugles" themselves. Thanks to this sound effect, readers can almost hear the buglers loudly "Blow[ing] out" air through their instruments.
The second sentence of the poem (lines 2-3) both begins and ends with alliterative phrases: "There's none of these" and "rarer gifts than gold." Nearly every subsequent line contains some alliteration as well. It's as if the music invoked in the first line carries over into the rest of the poem, creating a highly musical whole.
In fact, the second stanza begins by repeating the alliteration that kicked off the first—and throws in two extra /b/ words for good measure:
Blow, bugles, blow! They brought us, for our dearth,
The intensified alliteration signals a heightening of the poem's emotions, as the speaker demands music worthy of the soldiers' sacrifice. In general, this second stanza is even more lavishly alliterative than the first, from the opening phrase right through the ringing final words:
And Nobleness walks in our ways again;
And we have come into our heritage.