It's four guns on the starboard side, two on the port side. The original proposal had been for four in each wing but the landing lights in the port wing would have had to be moved, so to avoid further redesign the asymmetric layout was adopted. The first 50 Mk I aircraft only had cannon, after that all aircraft with 0.303 wing guns had the same layout (they were omitted on some models for less weight or to carry additional fuel); the Australian Mk 21 had .50 caliber wing guns, two in each wing.