After the Lord destroyed the forces of Gog, the Israelites would use the enemy"s numerous implements of warfare for fuel for seven years. The Israelites would not need to burn traditional fuel because there would be so many old weapons and implements left to burn. They would also take as spoil what the invaders had brought into the land when they came to despoil the Israelites. God would turn the tables on the invaders. [source][source][source]
As in much apocalyptic prophecy (cf. the Book of Revelation), the Lord revealed to His prophet what would take place in pictures that were familiar to him (i.e, contextualized revelation). This language does not preclude the use of modern implements of warfare in the fulfillment. Here the meaning seems to be that there would be so much combustible material utilized in the invasion that the Israelites would burn it for seven years. [source][source][source]