MV Glen Sannox - which was meant to be delivered almost seven years ago - is the first new large vessel to join the UK's largest ferry fleet in nearly a decade.
It made its first scheduled journey between Troon in South Ayrshire and Brodick on Arran before dawn, coping with rough conditions that kept other ships in port.
The vessel will make three return sailings each day, with the journey lasting 75 minutes, helping to end years of uncertainty on one of Caledonian MacBrayne's busiest routes.
With space for 127 cars and 852 passengers, Glen Sannox brings much-needed extra capacity for the state-owned ferry operator which has struggled in recent years to maintain services with ageing and increasingly unreliable vessels.
The orders for the dual-fuel ships Glen Sannox and its sister vessel Glen Rosa, were placed with the Ferguson shipyard in Port Glasgow nearly a decade ago.
But acrimonious disputes over the design challenges and claims for extra costs saw the shipyard fall into administration and nationalised in 2019.
The ships have ended up costing more than four times the £97m contract price and sparked arguably the longest running political row of the devolution era.