After a protracted dispute between the government and the drivers' trade union over their safety, they entered service on 3 December 2024 on the Central Coast & Newcastle Line.

[3][1][4] In May 2014, the Government of New South Wales announced its intention to purchase new carriages for the intercity network, then-operated by NSW TrainLink.

[21] A contract was let to Downer EDI to make modifications and upgrades to existing rail infrastructure across the electrified network to accommodate the new fleet.

[24] In July 2021, the Mariyung fleet received its final approval to carry passengers from the independent Office of the National Rail Safety Regulator and would enter service as soon as possible.

To achieve this top speed (a first for double-deck rolling stock in Australia) Hyundai-Rotem has supplied specially designed bogies & traction motor gearing arrangments, which results in a slightly lower acceleration when compared to the H set it is replacing.

This required works to provide additional clearance on several sections of the Blue Mountains line between Springwood, Katoomba, and Lithgow, including the heritage-listed Ten Tunnels Deviation.

[38][failed verification] In February 2020, the RTBU announced that members would refuse to staff the New Intercity Fleet over safety and employment concerns.

[39] On 27 November 2020, a strike in protest of the safety concerns was performed by the RTBU, shutting down all intercity services effective immediately until 7 am.

[40] A confidential 2018 report to the NSW government revealed that the doors could easily fail when opened at speed, which was only announced to the public in 2021.

[41] On 5 February 2021, an incident where a commuter fell between a train and the platform at Hornsby station in January was highlighted as a potentially fatal situation if it had occurred with a D set.

[45][46] On 22 March 2022, Nine News revealed the RTBU regarding the CCTV cameras as unsafe, highlighting the lack of microphones, viewing blackspots, and poor vision quality, especially in the rain.

[49] On 26 November 2024, the D sets were given approval to operate in passenger service with modifications on only the Central Coast & Newcastle Line from the Office of the National Rail Safety Regulator (ONRSR).

[52] In September 2017, the Central Coast Express Advocate opposed the Kangy Angy Maintenance Centre citing issues of noise and flooding.

[53] In December 2021, it was announced that only 20 out of 300 jobs would be made from the Kangy Angy Maintenance Centre, which was heavily criticised by several Labor MPs including Chris Minns.

[55] Despite this, during the testing and acceptance phase the operator made a decision to lower the permissible maximum service speed of the vehicles to 130 km/h.