I will present the results of our ALMA survey of the mid-J CO emission in 30 submillimetre galaxies (SMGs) in the ECDFS. We originally identified 870-micron submillimetre sources in LABOCA single-dish data, and over a period of ~10 years have collected extensive follow-up data on these targets, including ALMA band 7 imaging (for precise positions) and optical/near-IR spectroscopic redshifts (used to tune the CO observations). I will present the main results from this survey, including the resolved CO luminosities and the dynamics of the SMGs compared with lower star-formation rate populations. I will also present the serendipitous discovery of additional CO and 3mm continuum sources in many of the data cubes, and show that the component galaxies of blended SMGs (where one single-dish source is comprised of several galaxies) are typically separated by >2000 km/s but may be in different filaments of a protocluster.