The bayonet that Alder is talking about is what we are referring to as the Quillion Back. His statement above is 100% correct. With the blade at 15 1/8" it is a S98na that has been modified. If you look at the pommel and you see a crest it will be the Puruvian model that was exported from Germany to Peru and refered to as a M1909.
Semper Fi