'Diamond' was the British planning and construction of a dummy water pipeline as part of the 'Bertram' deception undertaking in preparation for the 'Lightfoot' opening phase of the 2^nd Battle of El Alamein (September/October 1942).

The undertaking was complete with fake pump houses and reservoirs, and extended across 20 miles (32 km) of the Western Desert to the rear of the XIII Corps of Lieutenant General B. L. Montgomery’s British 8^th Army, and the entire construction effort was carefully placed to suggest to the Germans that it would not be completed until a time after the planned launch of the real British offensive.