The British Rail Class 444 Desiro is an electric multiple-unit passenger train built by Siemens Transportation Systems in Austria between 2002 and 2004.

The fleet was originally painted in a mixture of SWT's express livery of white, with a blue window band, and red/orange swishes at the cab ends (although they replaced the South West Trains logo with a South Western Railway one, following their inheritance of the franchise), although all units have since received the new South Western Railway livery, which is predominantly light grey with darker grey sections towards the cabs, and doors painted in the opposing shade of grey to the bodywork in that area.

All seats have BS 1363 230 V mains sockets providing AC power for laptops or mobile phone chargers.

Like all new-build third-rail rolling stock in the UK, one car in each unit is fitted with a recess for a pantograph that allows for a future conversion to AC overhead power.

Both the Class 444 and 450 fleets are maintained at the purpose-built Northam Traincare Facility in Southampton, which is equipped to perform both preventative and corrective maintenance, deep-cleaning, and overhauls on up to eight units simultaneously.

[13] A new variable-stiffness hydraulic bush has been fitted to the whole Class 444 fleet so as to reduce track damage and thus infrastructure maintenance costs.

During twelve months, SWT's fleet has set a new reliability record of almost 89,000 kilometres per technical delay.

Previous power limitations meant that the trains were not permitted to run west of Poole; these restrictions have since been lifted.

[17] Class 444s are currently used on the following services: South Western Railway has conducted a refurbishment programme under its contract from 2017 onwards.

As part of this work, every unit has been deep cleaned, and the carpets and seat covers in standard class replaced.