Complex sentence: To the north, Leissegues closed with Brisbane's convoy during the night but did not close with it until the morning of 16 December, when Brisbane formed his three warships into a line of battle, accompanied by three of the larger merchant ships.
Split into simpler sentences: To the north, Leissegues gradually approached Brisbane's convoy during the night but did not close with him until the morning of 16 December. In response, Brisbane formed his three warships into a line of battle, accompanied by three of the larger merchant ships.