Castletownbere and Bere Island are beautiful! My husbands family is from the island. The harbor between the two is quite deep and able to shelter very large ships. It was here, that the French attempted to invade Britain in 1796 and there was a rush to defend the bay against further invasion. The British created the Martello towers on the island, construction believed to have begun in 1798.
Another significant event during that time period, the island suffered several famines and in 1822 particularly, due to a bad fishing season. A report was written 1824, now in the National Army Museum in London, describing the conditions by an army officer.
Just a few things you might consider in your research. Good luck!