Hello everyone I have recently came across an old flag while cleaning out some stuff in my house. I called and asked my mother to told me that its been around since shes been a kid so I dont really have a history of how It was obtained.

Its a pretty big size flag maybe 8 ft x 10ft or 12 ft  haven't officially measured just found it and wanted to learn more about it.  Its all blue with 48 white stars and on the side of the flag where it would be attached to a pole it has " Union Jack #4  March 1935 Mare Island"  written on it in the bold stamp lettering

Can anyone shed some light on what I have found here? Just looking for any info and maybe approx Value Not really looking to sell it just would be cool to know more about what I have found.

Thanks in advance.