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[Editor]

Hi all,

I was puzzled by this photo and the two small blisters visible where the upper wing roundels are. Another photo of the same a/c shows similar (but shorter) blisters below the wing.

Can anyone help me to identify the nature of this modification? Judging from the serial number, the aircraft appears to be a factory-fresh Spit Mk. VC of the earliest Supermarine production. I'd be grateful for any comments.





(Image source: http://www.spitfiresite.com/photos/historic/2009/03/aa963-in-united-states-colour-photos.html)

[Antoni]

They would appear to be the access covers for the outermost Brownings but why they have bulges is a mystery to me. Thinking of fitting 0.5s instead of .303s?

[Editor]

Well, that's the point. 0.5"s weren't the order of the day until much, much later. This a/c was produced in Nov 1941.

[Antoni]

There were some trials with electrical heaters for the Brownings but they were not adopted. Perhaps it was something to do with that.

[gilly617]

Hi Martin,

I don't think the small blisters were anything related to outer wing mounted Brownings as AA963 is a four-cannon Mk Vc and didn't have any. The Vc wing was the 'Universal' wing that gave a choice of armament. When cannon were fitted it was in one of two options. You could have a total (for the aircraft) armament of EITHER 2 x Hispano cannon plus 4 x Brownings, OR 4 x Hispano cannon and no MG's. The mixture of cannon and mg's was by far the most common as the four cannon option in the 'C' wing had problems with lack of heating for the outer pair of cannon resulting in stoppages at inappropriate moments. This configuration was also heavier and degraded aircraft combat performance so was not really popular with the drivers.

Of course there is always the possibility that this particular machine was fitted with the four cannon AS WELL as a couple or more Brownings, just to impress the Yanks, but I think this is unlikely as it would be even heavier still, and in the written text on the reverse of the last picture I sent you, the writer commented on its armament making no mention of machineguns.

If you look at the diagram of the 'C' wing on this website the small blister appears to be very near the position of the 'downward identification lamp', which might indicate they were something to do with access to service this item. The lamps were dispensed with on later marks.

I'll see if I can come up with anything better.

Cheers

Barry

[Editor]

I've been looking for some hint if the same bulges could be spotted on any other aircraft, and sure enough here they are. Another very early Mk. Vc, possibly tested by Air Fighting Development Unit , Duxford. You can see the shade of the blister on the white of the roundel, and also the silhouette of it in the similar position of the port wing.

Barry, I think that connection with outer Brownings cannot be outright eliminated, although I believe that the combination 4 cannon + brownings was never used. The early C wing was thought as a universal type, in which the armament configuration could be easily switched at the unit level without any changes to the wing itself - hence, for example, the wide cannon blister which was universally seen on aircraft with only two cannon. It is not impossible to think that Supermarine designed the blister there just in case the guns would be mounted.

Still no idea about their true function, though.
/Martin