In 1971, the Sedco 445 drillship became the first offshore drilling vessel to drill a well without anchors,  six years before the launch of the Sedco 709, the first semi-submersible to operate in dynamic positioning mode. One of the Shell companies saw a requirement for such a drilling rig and in March, 1974, entered into an agreement with SEDCO for construction of a new semi-submersible equipped with a station keeping system. In 1977, Sedco launched the Sedco 709, the first dynamically positioned semi-submersible oil drilling rig.
The Sedco 709 was an Earl & Wright Sedco 700 series was built in 1977 by Hawker Siddeley Ltd., Halifax Shipyard Division in Nova Scotia, Canada.
It could drill to a depth of 25,000 ft in 3,000 ft of water. It consisted of a 295 ft x 245 ft platform supported by 4 main columns of 30 ft diameter and four smaller columns of 19 ft diameter on two pontoons, and was 112 ft high. It completed trials in St. Margaret’s Bay in March 1977. After exploratory drilling on the Scotian Shelf until about 1986, it moved on to work in other parts of the world. In 1999 it received a major upgrade that allowed it to drill in 5,000 ft of water and had its accommodations increased from the original 91 to 124. After another refit in Capetown in 2006 it went back to work in Nigeria after working there and in Gabon and Angola.
In July 2013, Transocean advised that the Sedco 709 was cold stacked in Malaysia. In December 2014 the unit was officially withdrawn from operations and held for sale. (Image: Sedco 709 in Halifax harbour in 1977)