ESV - 13 When Gideon came, behold, a man was telling a dream to his comrade. And he said, "Behold, I dreamed a dream, and behold, a cake of barley bread tumbled into the camp of Midian and came to the tent and struck it so that it fell and turned it upside down, so that the tent lay flat.
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If one reads the next verses is actually gives the answer. The dream was like a word from God that He would give the Midianites into the hands of Gideon in battle. It does not look like a bomb. It may mean that Gideon will win the battle because God will help him.