The Carron office block was designed by Robert Baldie in 1880. Originally fifty three bays long, the central tower gatehouse, known locally as Thunderbird 3, is all that now remains. The ground floor has a moulded segmental pend arch; the first floor a triple window; and the second floor an armorial panel featuring the Carron Company seal. The tower is topped by a square clock turret and a pyramid spire. On either side of the pend, set into the front walls, are a furnace lintel from 1760 and a date plate from a boiler connected with James Watt. The pend is fronted by a wrought iron screen and contains two carronades and two 9-pounder long guns set on garrison carriages.