On the mainland in the north was in 1808–1809 built a defense battery which had the task to cover the land by Fredriksholm.

During the English Wars, three Royal Navy ships led by HMS Spencer arrived off Kristiansand.

After the Battle of Copenhagen, the only remaining ship of the line of the Royal Dano-Norwegian Navy was the 70-gun HDMS Prinds Christian Frederik, which was lying at anchor in Kristiansand's eastern harbour.

Spencer's captain Robert Stopford had earlier sent a letter to the Kristiansand authorities informing them that he had orders to capture Prinds Christian Frederik and threatened to bombard the city if the ship was not handed over.

When Roald Amundsen set out on the expedition to the South Pole in 1910, Flekkerøy harbor was last stop in Norway before departure.

At the fortress Fredriksholm nearly a hundred Greenland dogs stayed in anticipation of getting on board the Amundsen's ship Fram.

98 dogs (two had died along the way) arrived at Fredriksholm from Greenland on board the steamer Hans Egede on 4 July 1910.

The dogs were at Fredriksholm for a little over a month, until 9 August, when they were brought aboard the Fram at the start of Amundsen's South Pole expedition.