The M1 low pressure, Hawley fiber liners were the first type of liners issued with the M1 helmet in June of 1941. The earliest liner pattern featured a rayon webbing suspension and a fixed leather chinstrap with a square sliding buckle. The liners were made of compressed cardboard, wrapped in fabric and rolled at the brim. Because of this original liners were not very durable especially in damp or wet environments. The liners would quickly show wear, were easily dented and had a very short life span (these prop liners are made from molded plastic and are very durable). The Hawley liners were replaced with a more easily produced and more durable high pressure resin liner in 1943.
These are perfect for the earlier Solomon and New Guinea campaigns like Guadalcanal and other early events like the Allied invasion of North Africa. These liners will also sporadically pop up after 1943 since the US military used what stock they had left of them until supplies were depleted.