British Rail Class 484

The Island Line, an 8+1⁄2-mile (13.7 km) long rail route on the Isle of Wight between Ryde and Shanklin, has historically been limited in the type of rolling stock that can be operated due to clearance issues, particularly height of the Ryde Tunnel between Ryde Esplanade and Ryde St John's Road, which has had its trackbed raised numerous times over the course of its history to mitigate the risk of flooding.

These limitations continued even after electrification in 1966. Since electrification, the Island Line has used repurposed former London Underground stock, beginning with the British Rail Classes 485 and 486, built as 1923 tube stock, which were used from 1966 to 1989. Gauging trials took place in the 1960s to determine whether Class 503 units were suitable for use on the route, but without success. From 1989 onward, rail services were operated using Class 483 units, which originated as 1938 tube stock and last ran on the Northern line.

However, these units were first introduced on the Underground in 1938 and, by 2019, were more than eighty years old. This made them increasingly difficult to maintain, with the original fleet of eight eventually reduced to four in service, with another two retained as spares donors. As a consequence, replacement of the rolling stock became an urgent priority. This requirement was eventually linked with a wider need to invest in improvements in the line itself, and saw suggestions that it might be converted to a light rail operation, or even a bus rapid transit route.

However, in 2019, it was announced that the existing third rail operation would be retained, with a total of £26m invested to make improvements. A significant proportion of this would be used on the procurement of a fleet of new trains, which it was announced would be sourced from Vivarail's D-Train platform.

The first passenger-carrying Class 484 departed Ryde St John's Road railway station at 05:35 on 1 November 2021.

The Class 484 units are two-car trains built using the existing bodyshells and bogies of former London Underground D78 stock units modified for use on the National Rail network. These have similar features to the Class 230 trains from the same family, with Wi-Fi, power sockets and CCTV. The D78 Stock is similar in terms of height to other National Rail rolling stock in Great Britain and taller than the previous Class 483, and having undertaken a survey of the route, Vivarail confirmed that its proposed units were capable of traversing the Ryde Tunnel.

The first of the total of five units was due to be delivered for testing in the summer of 2020. The first unit arrived on the Isle of Wight on 19 November 2020 via ferry.

Each unit is formed of two Driving Motor vehicles.