The operation was conducted with the name as Operation Payback. On this operation about 19 high profiled sites of US defense belongs to US Army, US Navy, US Marine, and US air force have been taken offline for several hours.
Success of operation was announced by the group on their twitter handle @Anon_Centre. You can get the list of the site target by the hackers group in Pastebin.
You can check the screenshot which shows that Army.mil is offline for everyone.
Stay in touch with us, as we will update the post as we get further information on this.