Port Cornwallis is a port situated on Ross Island, off the NE coast of North Andaman. This should not be confused with Ross Island, which is opposite Port Blair, South Andaman.
Map of Port Cornwallis
There is a lighthouse, commissioned in 1973, near Port Cornwallis, "on the summit of Bopung Hill at the entrance of Aerial Bay."
References
Port Cornwallis Wikipedia(Text) CC BY-SA