The Boulton Paul Aircraft Company Ltd
The Avro Shackleton MR 1 Nose Turrets
The Air Staff of the post-war period realised that it was essential to provide a long-range anti-submarine aircraft , and after heavy losses from U-boat anti-aircraft fire in the Atlantic, heavy forward-firing armament was specified. The A V Roe Company submitted a variant of the Lincoln modified for maritime patrol work, which would be known as the Lincoln III.
Boulton Paul was asked to design a suitable nose mounting for two 20 mm (0.78 in) Hispano guns. The guns would have to be fitted to clear the radar scanner, mounted in the chin position. The company devised a powered installation giving a limited movement controlled by a sighting position in the glazed nose of the aircraft. The compact spherical mountings were fitted in barbettes either side of the nose, each armed with a 20 mm (0.78 in) Hispano Mk.5 gun with 300 rounds of ammunition. The guns were cocked with pneumatic chargng units, and both guns were controlled from a handle in the glazed nose section.
As was usual on these special mountings, the guns were sighted by the simple but effective Mk.IIA reflector sight, which although designed in 1936 remained in limited use until the 1970s. The 20 mm (0.78 in) rounds were fed from boxes in the fuselage, over the guns in flexible metal ducting, and taken into drum feed units on the guns.
The spherical mountings were enclosed in blister fairngs on each side of the nose. A mock-up of the mountings were built at Pendeford Lane, and found to operate successfully. However, the installation was modified whehn firing tests revealed excessive vibration. The installation was accepted for use on the Lincoln III, which was renamed as the Avro Shackleton MR.1* (See notes).
The above text and first two photos were taken from "British Aircraft Armament Vol.1: RAF Gun Turrets", by R Wallace Clarke. The last photo was taken from "Aircraft of the Royal Air Force since 1918", by Owen Thetford.
* Notes: After several years in service the nose of the aircraft was modified, the beam barbettes being deleted altogether. With this modification aircraft was then designated Shackleton MR.1A
In later versions of the Shackelton, the MR Mk.2, 2C & 3, a new longer, less bluff nose section was fitted, in which were housed two 20 mm (0.78 in) Hispano Mk.5 guns.
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