Ten city blocks of Manhattan became a river of black Sunday as 50,000 dark-clad ultra-Orthodox Jews took to the streets to protest Israel's proposal to force their young boys into its army. The gathering took up a stretch of Water Street, with demonstrators standing behind police barricades amid tight security as they prayed in solidarity with their brethren in Israel. 'These kids, a lot of them don't know how to hold a gun. They don't know what physical warfare is,' said Long Island rabbinical student Shmuel Gruis.