With the nearby No.23 Filling Factory at Chittening, plus the main plant at Banbury and a third plant at Hereford, construction of the chemical plant began at Avonmouth in 1917, but did not finish until 1923, costing £800,000. The plant came into operation from spring 1918, producing of dichloroethyl sulphide using the Despretz–Niemann–Guthrie process; the chemical agent was then placed into shells on site. Although the first product did not arrive in France until September 1918, two months before the Armistice, it was used that same month during the breaking of the Hindenburg Line within the Hundred Days' Offensive. By November 1918, Chittening had produced 85,424 mustard gas shells.