US Naval Nautical Flag, top area stamped, "1ST REPEATER SET 4 MARE ISLAND JUNE 1943".  Shows stains/dirt, wear, use. This measures 7 feet long and is 40 inches from the left and coming to a point at the end. Blue and yellow.  The flag of the First Repeater of the International code, is an accessory flag in Naval Comms.  The Flag is used to signal dangers.  Made of quality Cloth/Linen, shows double stitching and some light wear, staining.  
The Mare Island Naval Shipyard (MINSY) was the first U.S. Navy Base established on the Pacific Ocean.  It is located 25 miles from San Francisco Bay area in Vallejo, CA.  During WWII 50,000 people worked at the shipyard.  The base closed in 1996.  A very nice WWII Item.