Vandals have sprayed graffiti onto the walls of the Blyth Battery museum.
The wall of the south gun emplacement in Links Road was targeted by the vandals sometime between 5pm on Sunday, August 11, and 9.30am on Monday, August 12.
Lindsay Durward, secretary of Blyth Battery Volunteers, said: “On behalf of the Blyth Battery volunteers, we are so disappointed with the graffiti.
“We are trying our best to give Blyth a museum which we all can be proud of.
“We are free to everyone and hold events for the people of Blyth, most of whom are very grateful and enthusiastic.
“This time we have been able just of paint over it.”
Police are now appealing for witnesses to the attack.
A spokesperson from Northumbria Police said enquiries into the damage are ongoing and anyone with any information is asked to contact them on 101 ext 69191.