Although "Channel Firing" uses alliteration throughout, the device isn't always super noticeable. Sometimes, this is because repeating sounds are spread out subtly across the whole stanza, as with "While," "wakened," and "worms," in stanza 2, or "make," "Mad," and "more" in stanza 4. Other times, sounds repeat across quieter words that don't stand out too much, such as the /th/ sound in stanza 5 (both voiced and unvoiced), in words like "That," "this" and "thing."
There are some moments, however, where alliteration does make more of an impression, offering poetic emphasis on important images and phrases. For instance, the poem begins with alliteration on the important phrase "great guns." The /g/ alliteration draws attention to the guns, whose noise pervades the poem and is the whole reason for the conversation between God and the dead. Additionally, the alliteration adds a touch of irony. This is partly due to the artificiality of alliteration—it's not how people normally talk—signaling that there may also be something contrived about the very notion of "great guns." As the poem will go on to show, these guns are not so great; they're brute and foolish instruments of destruction.
The /g/ sound reappears in the third stanza in "glebe cow," "God," and "gunnery." Here, the /g/ triangulates three important elements in the poem. First, the "glebe cow," a parish cow, represents the helplessness and limited knowledge of individuals. "God," of course, plays an important role in the poem, revealing himself to be disappointingly limited and cynical, not the all-powerful benevolent deity he is imagined to be. And "gunnery" again reiterates the noise of the weapons. This trio of individuals–God–guns will thematically guide the poem.
In the last stanza, two instances of alliteration end the poem on a bleakly lyrical note. First, the /r/ sound repeats in "Roaring" and "readiness." The /r/ captures the "Roaring" sound of guns, once more returning the poem's focus to the loud guns. Then, /s/ and /t/ sounds repeat in "Stourton Tower" and "starlit Stonehenge." These sounds add some graceful musicality to the end of the poem. Whereas the middle stanzas have been ironic, lively, and bitter, this final stanza represents an abrupt change of tone. The poem grows much more serious and cosmic. The beauty of the phrase "starlit Stonehenge" has a kind of eternal mournfulness to it, as the reader considers how violence has played such a prominent role throughout human existence. The noticeable alliteration helps emphasize this.