national guard in the subways

what gives? we were on level orange alert last month and i didn't see one soldier... now we're on the more moderate level yellow, and tonight, on my way home from my friend's house, i saw four national guardsmen with m16s (the last time i saw national guard was at grand central and they didn't have guns) posted at the 6 stop on 59th and lex, and then two more at the union square station. service between times square and the brooklyn bridge was suspended due to "an incident" at canal street. anyone have details? [reposted to imc for further inquiry]