In the 50s and 60s, I have read, the Americans, although denying it, had to cross into Soviet or Chinese territory with the Orion to get a feed-back on the defense radar and then hurry back out again. Back then, radar was short range.
The USN and USAF were particularly active in Eastern Russia and also the Baltics, one shot down over Liepaja, Latvia, where recently there was a ceremony honoring the American crewmen who vanished off the face of the Earth, although some residents saw full chutes dropping down.
I wrote a news story about this in the mid-60s and as I remember it involved at least six incidents of U.S. intelligence planes coming in contact with MiG-15s to MiG-19s at the time. Most of those air crews also vanished.
Today, with all the modern equipment, we don't have to cross a nation's border to find out how fast they will respond or what we want to find out.
I firmly believe that the EC-3 was in international waters and this was a set-up by the Chinese. For goodness sake, we all have spy planes. Take a look at your own -- the Nimrod.
Iceland won the fishing war against the U.K. in the 70s, despite the Nimrod.