Originally Posted By EnigmaSammich:
ERDL went through some geometry and color palette changes during its Mid 1960s to 1981 issue life span. RRiggs, the pattern you have is one of the last iterations of the pattern right before adoption of the m81 Woodland that we are all familiar with. During and immediately after Vietnam there were two color palettes for the pattern, a "highland" or "brown dominant" option and a "lowland" or "lime" or "green dominant" pattern. Not only do you see the colors change slightly over time, but you also see a slight change of the shapes. Typical Vietnam ERDL has a sort of fuzzy definition between shapes, and as time progressed, the outlines of the shapes became sharper. Pictured from left to right are "green dominant" 3rd pattern jacket dated 68, "brown dominant" 4th pattern jacket dated 78, transitional ERDL dated 78 also and a true transitional jacket that shares the color palette with Woodland but the geometry of ERDL dated 80, which is cut like the Woodland BDU (which is a different cut than earlier jungle uniforms) From what I have gathered, the material used to make the ERDL helmet covers was never exactly like that available in uniforms, and the one you have is probably closest in resemblance to the later patterns. Vietnam dated helmet ERDL covers do appear from time to time, but the ones with late 1970s dates are all over the place.

http://s12.postimage.org/5xry2u4el/P1010022.jpg