 Israel dropped 18,000 tons of bombs on Gaza in 24 days. Selam Maruf, head of the media office of the government in Gaza, announced that the Israeli forces had dropped 18,000 tons of bombs on Gaza so far. This is one and a half times more than the atomic bomb dropped on Hiroshima. One of the most formidable challenges awaiting Israeli forces if they decide to invade Gaza is the Hamas Terror Metro, a network of hundreds of kilometers of tunnels that are used by Hamas fighters to carry out attacks and transport material. Hidden up to a 100 feet below the surface, the intricate city of passages is full of dark twists and turns, laden with traps and heavily reinforced with concrete. The entrances are enclosed under the floors of homes and mosques. Recognizing the need for an efficient way to take down Hamas fighters in their own territory, Israel is field testing sponge bombs which use a chemical reaction that explodes foam and can potentially be used to seal off tunnel openings. Israeli troops are said to have been practicing with sponge bombs on mock tunnels ahead of an expected ground invasion of Gaza. The Israeli army have not officially commented on their use of sponge bombs, however they are said to be currently testing the devices, said some media reports.