You must book these 1½-hour tours at least 24 hours in advance online or through your tour/bus company. Remember that the body of water you see at Deadhorse is Colleen Lake, not the Arctic Ocean. The only way to see the real thing is on this tour. You'll also get an intro to the oil extraction industry.
The tour starts early, but you can book it through the Dalton Highway Express to ensure you connect with your return bus heading south to Fairbanks.