Israel had carefully planned the invasion. A week of air strikes had prepared people on both sides of the border for what was to come; the only unknown was the weather. Days of rain had put the ground assault on hold; when the skies cleared, the army went into action.Thousands of regular soldiers, backed up by reservists called into service, moved across the border into northern Gaza. They had air cover, but there was little threat from above as Hamas has no planes, and the initial advance met few obstacles. The situation on the ground is unclear. The only television pictures are from the Israel side of the border; independent journalists are banned in Gaza, so there is no real picture of what is happening at the front. Israel’s firepower is overwhelming, but it may not guarantee victory. Hamas has vowed to turn Gaza into a graveyard, by fighting a guerilla war and trying to take hostages, much as Hezbollah did in Lebanon in 2006. Israel insists it has learned lessons from that conflict.