The museum's White Ensign flag was discovered missing on Remembrance Day.
A flag taken from the Niagara Military Museum in the Falls has returned.
Museum President Jim Doherty tells us "a great Samaritan" returned the flag and the halyard rope through the front door mail slot this morning.
He says the White Ensign flag was put on a flagpole outside the museum on Sunday, but had been taken at some point during the last few days.
Doherty says the flag was used by the Royal Canadian Navy from 1910 to 1965.
He also notes it's the first flag problem the museum has faced since it was opened in 2012.
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