See also Ferry fiasco for the political controversies surrounding the construction of these units.

The State-owned enterprise CalMac, originally Caledonian MacBrayne Ltd, was formed in 1973 as a vessel owner and operator providing most of the ferry services to the Firth of Clyde and the Hebridean islands off the west coast of Scotland. In 2006, its roles were split to satisfy EU competition rules. As Caledonian Maritime Assets (CMAL) it continued to own the Caledonian MacBrayne fleet and order new ships, while CalMac Ferries Ltd (CalMac) was created as a separate company which successfully bid in open competitive tender for the contract to operate the services. Many of CalMac's ferries had been built by Ferguson Shipbuilders, which five years earlier had employed 300 people, but it had struggled to compete and CalMac orders were won by the Remontowa shipyard in Gdańsk, Poland.^[16][17] In 2011 Fergusons successfully bid for two small ships for CMAL, funded by the Scottish Government's Low Emissions Hybrid Ferries project.^[18][16]

Transport Scotland's Ferries Plan, published in December 2012,^[19] included indicative proposals for two new vessels.^[20] International emissions regulations tightened, and cleaner liquefied natural gas (LNG) fuel was adopted by ferry operators in Northern Europe,^[21] particularly Norway. The Danish island of Samsø invited tenders for the first in the EU, and in June 2013 Remontowa was awarded the contract for this dual-fuel ferry, to be delivered in October 2014.^[2][22] David MacBrayne Ltd bid to operate a ferry connecting Gotland in Sweden, with detailed proposals drawn up by CalMac, but in May 2014 this bid was reported unsuccessful.^[23]

To prepare the Vessel Replacement and Deployment Plan (VRDP), Transport Scotland held tripartite monthly meetings with CMAL and CalMac, starting in October 2013. By agreement, CalMac led development of programmes for the major vessels.^[24] In early July 2014 the Scottish Government, using CalMac's initial analytical work, authorised the procurement process. It aimed to name the preferred bidder by the end of March 2015, leaving only three weeks to produce tender documents. CMAL's head of vessels said at the time it was a "hugely challenging" timetable. CalMac quickly adapted work done for the Gotland ferry bid to produce the Specification of Technical and Operational Requirements, but made some errors.^[16][20]

Glen Sannox is to be the first of two Scottish ferries capable of operating on either marine gas oil or LNG, with benefits of a marked reduction in carbon dioxide, sulphur and nitrous oxide emissions.^[1] Her name was chosen from a shortlist by public ballot and recalls an earlier Arran ferry.^[25]

The first steel was cut on 7 April 2016 and Glen Sannox was launched on 21 November 2017 by the then First Minister Nicola Sturgeon,^[26][27] It has been reported that the vessel's bulbous bow was not fit for purpose at the time of the launch, and only fitted to be able to claim "milestone payments" from the Scottish Government.^[28] The bridge windows were painted on,^[27] and the funnels were not operational, but only for show for the launch.^[28]

In August 2018, new Cabinet Secretary for Transport Michael Matheson said it had been confirmed that the ship was to be delivered in June 2019, followed by two months of crew familiarisation and sea trials.^[29] Further dispute over the contract overrun led to the shipyard going into administration and being nationalised by the Scottish Government.^[30][31]

A report produced after nationalisation indicated that Glen Sannox should be handed over to Caledonian Maritime Assets Ltd (CMAL) in the last quarter of 2021 and that completing the two ferries was likely to increase the total cost to over £207 million.^[32] In April 2020, Ferguson Marine contracted with International Contract Engineering, a marine design consultant, to revise the design and outfitting of Glen Sannox in advance of her eventual delivery.^[33]

On 10 August 2020, tugs moved Glen Sannox to the Garvel dry dock in Greenock for remedial work including replacement of the bulbous bow, paintwork repair and removal of marine growth.^[34] After additional work, the ship returned to the Fergusons shipyard in Port Glasgow on 9 September 2020.^[35]

In October 2022, it was announced that Glen Sannox would initially operate only on marine gas oil, as vacuum sensors required for the LNG system were not available.^[36]

Further delays to both ferries and increasing costs of £250 million, subsequently rising to £340 million by September 2022, have resulted in controversy surrounding the contract and the lack of transparency in the decision-making process.^[37][38] The Scottish Government announced that key documents relating to the decision-making process had gone missing.^[39]

In September 2023, a failed safety audit meant that MV Glen Sannox was further delayed: among other issues, the Maritime and Coastguard Agency (MCA) insisted on the installation of additional staircases as a condition of approving a safety audit. The work meant that planned sea trials of the Glen Sannox were delayed until the first quarter of 2024, raising doubts over whether the ship will be available for the start of the 2024 summer season.^[40] Meeting MCA safety regulations ultimately meant that the passenger capacity of both ferries had to be cut from a planned 1,000 to 852.^[3] The ship began manufacturer's sea trials on 13 February 2024.^[6]

Glen Sannox is being built for the Ardrossan to Brodick crossing. She was originally intended to serve as a running mate to MV Caledonian Isles on the Ardrossan–Brodick and the Ardrossan–Campbeltown crossings.^[7][8] In May 2023, it was announced that Glen Sannox's sister vessel, MV Glen Rosa, would also serve the Arran route.^[41] However, the two new Arran ferries will initially be operating between Troon and Brodick for the first two or three years of their career, due to the planned upgrade works for Ardrossan harbour.^[42]