How many guns did a Sunderland eventually carry?

Following comments from the Air Ministry and the Royal Air Force, it was decided to fix the defensive armament at a single Vickers K .303 in the nose turret and four Browning .303s in the tail turret. At the end of 1940 two Vickers Ks were added in new hatches opened in the upper sides of the fuselage, just behind the wing, with the corresponding airflow deflectors. During the Sunderland II production run, the two side guns were replaced by an F.N.7 two-gun turret, the same one used by the Blackburn Botha. Late-production Mark IIs carried a dorsal FN.7 turret offset to the right, just behind the wings, with two .303 machine guns.

Much later a two-gun turret was planned in a dorsal position, on top of the fuselage and roughly level with the trailing edge of the wing, raising the total defensive armament to 16 machine guns.

The ASV Mk II radar required eight transmitting antennas on each side of the hull, four dorsal dipole receiving masts and Yagi homing arrays in the centre and under the wings, so that the Sunderland was truly bristling with spikes. The Germans are said to have nicknamed it Fliegendes Stachelschwein, "flying porcupine", because of its defensive firepower. On 3 April 1940, a Sunderland operating off Norway was attacked by six German Junkers Ju 88C fighters: it shot one down, damaged another enough to force it to withdraw and later make a forced landing, and scared off the rest.