The British lost some 90% of their stock of Bren light machine guns in the disastrous Dunkirk evacuation, and in the following months rushed to rearm. Part of this program was a two-tiered simplification of the Bren design. First was a MkI Modified Bren (which was not marked any differently than the original MkI), and this was followed by a MkII design. These patterns simplified many of the machining operation required to produce the Bren, significantly reducing the number of required machining operations. The most visually distinctive elements of the MkII pattern were the omission of the stainless steel flash hider assembly and the replacement of the original dial rear sight with a simple ladder sight. In addition, changes were made to the buttstock, buttplate, receiver profile, gas block, and bipod. Both Enfield and Inglis would produce the simpler MkII Brens by the middle of the war. Despite the many changes made, the core operating components (bolt, bolt carrier, etc) were left unchanged, so they could still interchange between all patterns of the gun in service.