This is a boa liner for the M-51 (M-1951) field parka, adopted by the US military in the 1950s. There are two types of liners for the M-51: this boa type and a pile fabric type. This is a rare early model. The size markings have faded, but the fit is similar to a regular XL size in clothing. As it is old, there are noticeable stains and dirt on the lining. However, the boa side also shows faint stains and black or brown spots, but there are no tears. There is a hole of about 1 cm on the lining, but nothing major. US ARMY Wool Military Vintage