The roll-on roll-off ferry Riverdance, which crosses the Irish Sea twice a day, was carrying trucks and trailers from Warrenpoint in County Down to Heysham in Lancashire.
The vessel ran into trouble after it was hit by a freak wave. Helicopters from RAF Valley in Anglesey captured the stricken ship using night-vision camera equipment.
Three helicopters - one from the navy, one from the RAF and one from the coastguard - were sent to the scene, as well as RNLI lifeboats.
There were 14 people airlifted to safety, but nine crew members remained behind.
At one point the troubled vessel was listing dangerously at a 60 degree angle.