In May 1968, an order for 212 cars (35 6-car trains, plus a spare car) was placed with
Metro-Cammell of
Washwood Heath to replace
O Stock and P Stock on
London Underground's
Circle and
Hammersmith & City lines for delivery from 1969, but trials of a four-car unit were delayed until summer 1970. The
C69 stock first entered service on 28 September 1970. For the name of the train, the letter C was chosen as the train would be used on the Circle line. The C69 stock was constructed using the then-standard form of a load-bearing aluminium underframe with a non-load-bearing body of riveted panels on aluminium framing. The high-density nature of the Circle line service meant that loading times were important; consequently all cars were fitted with four double sets of air-operated sliding doors per side. Seating was mainly transverse, and total seating capacity was 32 per car. The 106 DM cars (Nos 5501-5606) were each coupled to one of 106 T (Nos 6501-6606) forming semi-permanent two-car units, with an automatic coupler at each end. Three such units were then marshalled as six-car trains for normal service. The DM cars were slightly longer to accommodate the drivers' cabs, the saloon dimensions in all other respects being the same. To replace the
CO/CP stock on the
Edgware Road to
Wimbledon section of the District line, a further eleven trains designated
C77 were ordered of identical layout. The 33 DM (Nos 5701-5733) and T (Nos 6701-6733) were also formed as 2 car units and could and did interrun with C69. The first was delivered in July 1977, and entered service in December 1977. Equipment as built included load sensing "Metacone" air suspension, rheostatic braking, hydraulic parking brake, pneumatic camshaft control by GEC and Brush DC motors of type LT117, with each Dm car having four motors. Air supply was by Reavell reciprocating compressors and braking equipment was by
Westinghouse. The guard's door controls were in the driver's cab; this eased conversion to one-person operation in 1984, the first LU line to do so. One additional DM car was added to the C77 order to replace C69 DM car 5585, which had been damaged in the
West Ham station attack in March 1976. The replacement DM car retained the 5585 number and 5585-6585 therefore became a hybrid C69/C77 unit. Unit 5606–6606, which had been used for various equipment trials, was scrapped in 1993. Cars 6505 and 6713 were damaged in the
7 July 2005 London bombings and were scrapped above the solebar. The remains were used in the building of new cars 6606 (the second car with this number) and 6734 as C08 stock. They were paired with 5505 and 5713, renumbered 5606 and 5734 to match their partners. 5548+6548 were rebuilt in part following the bombings. == Design ==