Originally a pattern 13 built for Britain by Remington (For the Pattern 14 rifle) in Oct, 1917. Britain had contracted Remington and Winchester to build the P14
With the British inspection proofs cancelled and the "US" stamping it appears to have retained by the US army for use with the US Rifle Model 1917 (which is externally identical to the P14 but chambered for the 30-06 round).
America was very short of small arms in 1917 and turned to the Model 1917 to arm most of the US expeditionary force headed for France.
This bayonet is missing the pommel along with the locking mechanism.