Production capacity at these two vital war plants was raised to a total of 66,000 tonnes of magnesia a year by 1942. During the War, Magnesium Elektron manufactured more than 80% of the magnesium products made in Great Britain Sea-water magnesia played a huge role in this.

Harrington works closed at the end of WWII due to a fall in the the demand for magnesium metal. Cost of production became important once wartime 'necessity and economics' no longer applied.

During 1951 the government restarted Harrington works to produced refractory grade magnesia for the steel industry. Major operational problems were encountered due to the rotary kilns having no separate coolers to handle the extremely hot magnesite product. The Redler conveyors which were adequate for reactive magnesia powders were unable to cope. Higher temperature operations also brought about an increase in the chimney emissions over Harrington. An off-white dust covered large areas of the town.

Steetley was allowed to re-acquire the plant during 1952. From the end of the War to 1952 the improvements made in the Hartlepool operations greatly exceeded the development potential for the Harrington works. For both economic and environmental reasons the Harrington Shore Works was dismantled in 1954.