Summary
This segment of the poem begins by continuing the enjambed phrase that started in line 15. While line 15 ended with the words "spits like a tame cat," line 16 finishes that phrase, bringing context to it with the words "turned savage"—in other words, the storm makes the sea spit against the windows, the same way that a tamed cat who has become angry or rabid might. However, the speaker says, they and the other people on the island can do nothing but sit and wait while the storm attacks, the wind diving down and swooping like a plane, though it cannot be seen. The space around them becomes a "salvo," meaning a sudden discharge of gunfire. The people of the island are attacked by the very air around them. The speaker notes that it's strange how the islanders' fear is of empty space—which is, essentially, the same as being afraid of nothing.
Analysis
Up to this point, we've already seen how this poem functions through contrast and unexpected binaries—broadly speaking, we can think of it as a sense of "two-ness," with opposites and parallels driving the poem's tension. We've seen, throughout the poem's first 15 lines, a portrayal of a world divided into only two categories: islanders and non-islanders. But that tendency towards juxtaposition and paradox absolutely explodes in these final four lines, expressed in a variety of ways, none more prominent than Heaney's articulation of the paradoxical relationship between emptiness and force.
Within these final four lines, we first encounter this idea of binaries in the phrase "turned savage," which initiates line 16. This completes the phrase that started in the previous line, and, using the tool of enjambment, suddenly contradicts it: we go from "tame" to "savage" in the space of a few carefully split words. Indeed, the first word of the line is "turned." The choice to start the line with an active, physical verb (even though, in this particular context, it's meant in the non-literal sense of "became") makes us feel caught up in the poem's action. The fact that this active verb can also be used to mean "switch directions" mildly foreshadows all of the two-ness, the juxtaposing of opposites and paralleling of similarities, that is to come.
But the most important and noticeable example of this two-ness is the paradox, which the speaker takes note of in these final lines, that the storm can be incorporeal and invisible yet frightening and powerful. For instance, take Heaney's description of wind in lines 16-17: it "dives" and "strafes," but it does those things invisibly. Diving is a verb we tend to associate with people or animals, but the word "strafe" is an import from the lexicon of war and the military. It's used, most of the time, to refer to the repeated assault of a military plane. The use of this word usually evokes a solid, very tangible piece of aircraft, so using it to describe wind, and pairing it with the word "invisible," introduces a tension: how can something as intangible and indefinable as the wind act like a metal plane dropping bombs? Right after this description, Heaney hits the reader with another paradoxical image: "Space is a salvo." A salvo is another word drawn from military vocabulary. It refers to a repetitive bombardment of artillery. Once again, we see a juxtaposition of space, the vaguest and most incorporeal concept possible, and "salvo," a term rooted firmly in the world of physical force and materiality. With two rhyming lines, the speaker brings the poem to a close, acknowledging the paradoxical nature of the situation by saying that it is "strange" for the islanders to be so afraid of a "huge nothing." This, indeed, actually brings us full circle to the beginning of the poem, when the speaker described the solidity of the islanders' houses and landscape. By the end of the poem, we're left to marvel at how something so solid and weighty can be threatened by a storm, which is in a sense just a "huge nothing."
There are multiple ways to interpret this idea of fearing emptiness, all of which can (and probably do) exist simultaneously. One, the most literal, is simply that Heaney is trying to capture an odd and elusive aspect of physical reality—the fact that something can be incorporeal and, at the same time, forceful. Then there's a broader metaphorical interpretation: maybe Heaney is trying to make readers think about how things like war and conflict can exist on multiple levels, both as abstract concepts and as incredibly destructive realities. Finally, there's the possibility that this poem is a specific historical allusion to conflict in Ireland. The military vocabulary that is used here certainly points towards such an interpretation. Viewed through this lens, Heaney may be commenting upon the fact that, while abstract cultural, religious, and historical divides have created the context for the violence in Ireland, the violence itself is as real and tangible as can be. Furthermore, his identification of the storm as a "huge nothing" may be a barb aimed at British rule. That ruling power, the poem suggests, is dangerous but essentially empty, without meaning or importance.
