I think there is a long history of naval visits in Hongkong. When I was there in 1998, there was a US warship at the Ocean Terminal. It was a carrier for large helicopters and other stuff for a seaside invasion. I even managed to get a guided tour on that ship. One of the marines told me that they do a "cruise" when the crew is new on the boat. That ship was based in Japan and sailed down to Hongkong for some days as a excercise.
When I was back there in november 2000, a French warship was in Hongkong, also standing at the Ocean Terminal, in the middle of the city.
Well, my visit on USS Dubuque back in 1998 was long before the attack against USS Cole and also before 9/11. I don't think that it would be possible to get on those ships as tourists now.