You appear to be able to launch missiles, so you probably already know this, but it caught me out for a while: you must put the missile 'pipper' over the target so that you're pretty much pointing right at it. Seems a little crude in comparison to most modern missile systems.
Also you must hold the 'release weapon' button down for a second, but you say you aren't getting the 'C' symbol so that's not the problem but I thought I'd mention it.
Cheers,
Dan