Alliteration is used sparingly throughout "Kamikaze."
An early example is in lines 4 and 5:
full of powerful incantations
and enough fuel for a one-way
The two /f/ sounds here both relate to things that the pilot needs with him for his mission: fuel and conviction (a head "full of powerful incantations"). Both words are also echoed in "powerful." The incantations—kind of like spells or affirmations—are meant to provide the pilot with the metaphorical fuel of the mind that will allow him to follow through with his suicide mission.
There is also some subtle alliteration in the following stanza. Though the words are on different lines, the shortness of these lines means that the /b/ sounds in this stanza chime together ("boats," "bunting," "green-blue"). "Strung" and "Sea" also ring out alliteratively, and the effect of all of these sounds is to give the stanza a kind of sonic sparkle to match with the visual beauty of what the pilot can see from his plane.
The sounds in the following stanza achieve a similar effect, with alliteration used in line 17 and 18, the end of stanza 3:
flashing silver as their bellies
swivelled towards the sun
Again, this seems to brighten up the line, matching the poem's sound to the pilot's view.
Stanza four is full of alliteration. Line 21 uses /p/ sounds in "pearl-grey pebbles," which evoke the stacks of stones that the pilot and his brothers used to make. Later in the stanza, /b/ sounds convey the pilot's memory of his father's boat disrupting the water—causing "breakers" (which alliterates with "bringing" and "boat").
Though there is some alliteration in the last stanza, the final key instance is in line 36, the last line of stanza six. This stanza talks about the way that the pilot was disowned by his family because of the shame he brought on them by not completing his kamikaze mission. Accordingly, it is generally somber and sober in tone, contrasting with the vivid and lively language earlier in the poem. But there is one example of alliteration that stands out tonally, line 36: "only we children still chattered and laughed." There is a playful sound to this loud and clear alliteration, relating to the way that the children—unlike the adults—don't really care for the system of shame and honor that makes the pilot's life miserable. Unfortunately, as the next few lines reveal, they do learn "to be silent" and ignore his love.