In July 1997, North West Trains placed an order with Alstom for 27 sets. The original order was for eleven two-carriage units with a top speed of 100 mph, seven three-carriage units with a top speed of 100 mph and nine three-carriage units with a top speed of 125 mph. This was reconfigured to eleven two-carriage and sixteen three-carriage units all with a top speed of 100 mph. As they were constructed, the old locomotive sheds at Chester were replaced with a purpose-built facility in order to service the Class 175 units. Units were tested at low speed at the Severn Valley Railway before further testing and driver training at the Old Dalby Test Track from November 1999. The first unit entered service on 20 June 2000. The two-carriage units are numbered 175001-011, and the three-carriage units 175101-116. Carriages are labelled as coaches A-B-C, with two-car units having no coach B. Each train has provision for two disabled passengers in coach A, and storage for two bicycles in coach C. Early reliability problems meant that some services were operated by old rolling stock at short notice. Remedial work included improving brakes and bogies, and the reliability of the units is now greatly improved. Class 175 Coradias are fitted with a passenger information system, which consists of onboard LED display and audio announcements of train destinations and arrivals.
On 16 January 2010, 175103 operating the 08:30 service from to struck two cars at Moreton-on-Lugg crossing between Hereford and Leominster. The front seat passenger in one of the cars was fatally injured, although there were no casualties on the train. The train did not derail. The signaller had raised the barriers in error when the train was approaching the crossing, and he was arrested on suspicion of manslaughter in July 2010. The same service collided with a trailer on the Morfa Main level crossing near Kidwelly on 31 January 2011. No-one was injured, but the unit involved, 175108, received nearly £82,000 worth of damage due to striking the trailer at. The farmer in charge of the trailer was sentenced to a 36-week suspended jail sentence and was ordered to carry out 200 hours of community work. On 19 December 2011, 175002 collided with a lorry at the Llanboidy level crossing near Whitland. The train was operating the service from Milford Haven to Manchester Piccadilly and the driver of the lorry was arrested on suspicion of endangering safety. Class 175 units have caught fire in 2004 at , 2009 at, 2011 at Manchester Piccadilly, 2017 both at Shrewsbury and between Chester and Crewe, 2018 at Deganwy, and in 2019 both near Pontrilas and at Gowerton. In February 2018, the entire Class 175 fleet was temporarily withdrawn from service for safety checks. After further investigation, it was found that a track fault between Newport and Cwmbran had caused wheel damage to several class 175 units, and also some Class 158s.
175116 - Peter V. L. Jones, Community Rail Officer Conwy Valley Line
All except forEisteddfod Genedlaethol Cymru were named by First North Western. The nameplates were all removed in 2009 when the fleet was repainted into Arriva Trains Wales livery.
