WWII German Kriegsmarine Navy Command Pennant Streamer flag, sometimes called a "Commander Pennant". These were one of many command flags used by the Kriegsmarine while vessels were underway, or even when they were still in the yard. This particular style, was typically displayed only when entering port or while docked, attached to the naval flag.
It feels like it is made from a wool or wool cotton blend body, the header surrounds a halyard rope loop. The design features a printed Kriegsmarine Navy black Tatzenkreuz (cross pattée) with a white border, used on Kriegsmarine command flags and pennants. It is very thin, with a swallowtail end, as it was intended to attach to other flags. This example has certainly been used on the high seas and is showing signs of heavy use. The pennant measures approximately 1150mm in length.
This is the only example I have ever seen making them rare, a great display item for the avid Kriegsmarine collector.