The walls of Worthing's Territorial Army Centre have been daubed with anti-war slogans.
Vandals painted "No Racist War" and "Free Palestine" on the building in High Street.
Peace demonstrations were held in the town throughout last week, culminating in a major protest through the streets on Thursday night.
A police spokesman confirmed officers had taken pictures of the graffiti and said the culprit had "jumped on the bandwagon" of the demonstrations.
The TA's Captain Andrew Layzell said: "It's senseless vandalism. What do they hope to achieve by doing this?
"It was done not in the glare of publicity but in the early hours of the morning - it's mindless.
"A police investigation is being conducted and the graffiti will be removed but at more cost to the taxpayer."
The centre is the home of The Princess of Wales' Royal Regiment, 6 Platoon B Company.
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