When they were backing the contras they flew the coke in themselves as far as I know, used shell companies to charter planes etc to try to put some distance between themselves and what they were doing but they didn't try to hard. There is a really good docco called last great white hope (I think that's the correct name) that covers this issue, in 1996 Gary Webb wrote a series of articles published in the San Jose Mercury News, which investigated Nicaraguans linked to the CIA-backed Contras who had smuggled cocaine into the U.S. which was then distributed as crack cocaine into Los Angeles and funneled profits to the Contras. CIA Director John M. Deutch went to Los Angeles to attempt to refute the allegations raised by the Webb articles, and was famously confronted by former Los Angeles Police Department officer Michael Ruppert, who testified that he had witnessed it occurring. It is one of the best moments where someone is called out in the most public way and has nothing to come back with. Yes I got some of that from Wikipedia but watch the docco, it's very good.