Complex sentence: Cammell of Birmingham to replace O/P Stock on the Circle and Hammersmith & City lines for delivery from 1969, but trials of a four-car unit were delayed until summer 1970.
Split into simpler sentences: Cammell of Birmingham to replace the O/P Stock then used on the Circle and Hammersmith & City lines. Designated C69 stock in the hope the first delivery would be in 1969, trials of a four-car unit were delayed until summer 1970.