Rashi: They are the bows of Sancheriv and his multitudes. This is unlike "Rishpei Esh" (Shir ha'Shirim 8:6, i.e. coals); it does not apply to bows. Also, here the Fei has no Dagesh, and there it is Pei with a Dagesh. Here it is like "u'Lechumei Reshef" (Devarim 32:24); the Targum of Reshef is Ohf. It says also "u'Vnei Reshef Yagbihu Ohf" (Iyov 5:7); "u'Mikneihem la'Reshafim" (below, 78:48) refers to birds. "U'Vnei Reshef" are Shedim; Yagbihu La'uf (they fly). Also here, arrows fly - "me'Chetz Ya'uf Yomam" (91:5). Our verse teaches that He broke arrows that the bow made them fly.

Radak: They are the arrows and the bow.

Radak: Hashem will break all the Goyim's weapons in that war [of Gog and Magog].

Malbim: Sancheriv went with bows, swords and war to conquer the entire world. When he reached Tziyon, Hashem broke his weapons ¹ , and the entire land was serene.