The Island Line, an 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 and , 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 units were suitable for use on the route, but without success. From 1989 onward, rail services were operated using 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. ==Design==