Employees celebrate the opening of The Gap Factory store at Arsenal Yards. The Gap Factory store officially opened for business in Watertown on Wednesday morning. It is the first new store to open, or in this case, re-open, at Arsenal Yards. The Gap Factory had been one of the tenants of the old Arsenal Mall. The store joins Marshalls, which remained open during construction, as places available for shoppers to visit in the redevelopment of the old mall.