The Siemens C651 was the second generation electric multiple unit rolling stock that operated on the North–South and East–West lines of Singapore's Mass Rapid Transit (MRT) system.

These trains were manufactured by Siemens Mobility (SIE) and SGP Verkehrstechnik in Vienna, Austria under Contract 651.

Unlike the 66 first generation Kawasaki Heavy Industries C151 trainsets, the C651s were delivered with a scratch-resistant acrylic finish.

This alleviated the difficulty of removing dirt trapped on the exterior surface, as opposed to the aluminium finish of the C151 trains that were delivered unpainted.

Other original features included specifically designed air-conditioning vents that eliminate dripping from the cooling system to the train compartments, as well as an event recorder, which records important train functions, such as braking and emergency operations to assist troubleshooting in an event of a failure.

[2] When completed, these upgrades would have addressed components such as doors and brakes that have been the primary cause of delays owing to train faults.

In July 2024, it was revealed that parts from a decommissioned C651 trainset (set 215/216) such as train doors, seats and map displays are being preserved at the National Museum.

[4] These are the trains that are preserved:[additional citation(s) needed] Incidents C651 Door Dislodged 15 December 1997 (4:15pm) - A C651 trainset was undergoing modifications at Bishan Depot by Siemens before being deployed for the evening peak period.

[17] Ang Mo Kio Siding Derailment 13 April 1999 (10:00 am) – An off-service C651 (set 227/228) was on its way back to Bishan Depot after running during the morning peak period.

A complete six-car trainset consists of an identical twin set of one driving trailer (DT) and two motor (M) cars permanently coupled together.