Episode #1.4 - S1-E4
Continuity mistake: The captain of the submarine has the rank of Commander (3 solid stripes) and half-way through episode 4 the captain suddenly has the rank of Captain (4 solid stripes) as shown on his shoulder epaulettes.
Continuity mistake: The captain (who holds the rank of commander) is in some scenes wearing four rank rings instead of the correct three he wears for the rest of the series.
Continuity mistake: Kirsten is referred to as a DC (Detective Constable) in the first half of the series and then as a DS (Detective Sergeant) in the second half. As these later episodes include flashbacks to before the previous episodes, she obviously hasn't suddenly been promoted.