I do love a good flying boat. The RAF Museum's Sundy Mk.V and its gun positions visible.
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Before we look at the guns on this beastie, it's worth noting that the Sunderland was considered for a variety of armament changes that didn't happen, but were planned owing to the U boat threat, including larger calibre guns in different turrets, such as the Curran Brockhouse CBI turret armed with two 50 cal Brownings in the nose, which was eventually fitted to the Seaford, but not the Sunderland, and a single 37mm Vickers gun in an open nose position instead of the turret. Another scheme saw two Vickers guns mounted vertically and aimed downward to emerge on the planing bottom, but this was impractical. A forward firing Vickers 40mm S Gun was also considered for the nose position, but the Sunderland was never fitted with it because of the work required in strengthening the nose section to house it. A Nash & Thompson quad 50 cal Browning armed mid upper turret was also planned, the FN.36, but this was cancelled.
The nose guns, with four fixed forward firing .303 Brownings and a Nash & Thompson FN.5 turret with two .303 Brownings.
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The four fixed guns were fired by the pilot from the cockpit and were first used by a 10 (RAAF) Sqn Sunderland and became standardised in Sundy Mk.Vs, as seen here. Early Sunderland Mk.Is and IIs had FN.11 single Vickers gun nose turrets, within which the gun was offset to the side to enable the gunner to serve as an observer also. The FN.5 was standardised on British bombers, such as the Wellington, Manchester, Stirling and Lancaster, so it made sense for it to be fitted to the Sunderland.
Sunderland Mk.IIIs were also fitted with a Vickers .303 inch K gun in their galley hatches, I'm presuming it's the square opening forward of the bomb bay cutout under the wing in the picture below, which was an emergency exit located in the galley on either side of the central walkway through the aircraft.
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This is the port side opening for the beam guns, which were nominally .303s, but in Mk.Vs these were often removed and the positions used for observation.
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This is what the inside of the rear fuselage looks like at this point; a bit more space for the gunners than the early model Sundy Mk.Is, that Green Knight posted a piccie of. This was taken inside a former RNZAF Sunderland V undergoing restoration and I talked to a guy who formerly served as an Observer/Air Gunner aboard the RNZAF Sunderlands and he explained that although trained as an air gunner, during anti-submarine patrols, the gunners in this position served primarily as extra sets of eyes, as even though the Sunderlands were fitted with radar under the wings, the Mk.I eyeball was (and still is in traditional maritime patrol aircraft) a good sensor for close in submarine detection despite increasing sophistication of ASW equipment post-war. It's worth noting the RNZAF retired the Sunderland in 1967, the last fulltime operator of the type, to replace them with P-3s; a huge leap in capability.
Sunderland Rear Gun positions
In this side view, above the beam positions can be seen the flat for the top turret, which in the Sunderland Mks.II, III and early Vs was a Nash & Thompson FN.7 turret, a woeful thing that gunners didn't like at all and contributed to aerodynamic problems in the Manchester bomber.
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This is an FN.7 cupola.
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Finally, Sunderland Nash & Thompson FN.4 rear turret armed with four .303 Brownings. The first tail turret the Sunderland Mk.Is were fitted with was the FN.13, which was designed especially for the Sunderland, like the Vickers gun equipped nose turret, to enable the gunner to serve as an observer.
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The Sunderland was the first maritime patrol aircraft fitted with power turrets and one of the first 'bombers' of any type to enter service with power turrets fitted as standard armament, the unique thing with the Sunderland being that the turrets were not just defensive in nature, but served an offensive purpose, with the aim of attacking submarines, as much as defending itself against air attack,