But recent intelligence has shown the extent to which Hamas has been able to build many of its rockets and anti-tank weaponry out of the thousands of munitions that failed to detonate when Israel lobbed them into Gaza, according to weapons experts and Israeli and Western intelligence officials. Hamas is also arming its fighters with weapons stolen from Israeli military bases.

Intelligence gathered during months of fighting revealed that, just as the Israeli authorities misjudged Hamas’s intentions before Oct. 7, they also underestimated its ability to obtain arms.