Avro Manchester Rear turret

[Selwyn]

Have some conflicting information.

its generally stated that the Manchester was fitted with the FN4 rear turret. This turret was un-armoured and had limited ammunition as it was stored in the base of the turret.

The Lancaster used the FN20 turret which was an modified/updated version of the FN4 and was fitted with  armour and an improved external ammunition feed system, that allowed for a much larger supply of ammunition.

However whilst looking at this I found that Tony Buttler in warpaint 103 stated that only the first 20 Manchester airframes used the FN4, the rest were fitted with the FN20.  Along with this I also found when looking this picture of the Manchester interior  from world war photos.   It clearly shows fuselage mounted ammunition tanks and feed tracks to the rear turret. These items were only used with the FN20 turret, as stated before the FN4 Am.munition was kept in the turret. Its not a Lancaster image as the Lancaster used a different style of ammunition tank.

 

Can anyone provide any further information relating to this mystery?

 

[Graham Boak]

I don't see how there could be room inside the FN4 for the ammunition.  So this could be one, as far as I know.  However it should be reasonably easy for Manchester enthusiasts to look at enough photos to find later Manchesters with the FN4, if they existed.  A better source might be the recent Wingleader - certainly another good one.  The now veteran Midland Counties book on the Manchester has been reprinted, and could be the best of all.

[Finn]

Here is another photo:

 

 

Jari

[Selwyn]

1 hour ago, Graham Boak said:

I don't see how there could be room inside the FN4 for the ammunition.  So this could be one, as far as I know.  However it should be reasonably easy for Manchester enthusiasts to look at enough photos to find later Manchesters with the FN4, if they existed.  A better source might be the recent Wingleader - certainly another good one.  The now veteran Midland Counties book on the Manchester has been reprinted, and could be the best of all.

he Nash & Thompson Type F-N.20 Tail Turret
This Turret was the most important of the Parnall Aircraft Ltd Range, providing Rear Defence for most of the Aircraft of Bomber Command.  The Designers at Oakcroft Road, Tolworth had been asked to re-design the F-N.4, incorporating modifications suggested by Gunnery Leaders on the Squadrons. An Armoured Shield was fitted & the Gunner was provided with a Clear-vision Panel, but the main improvement was in the Ammunition Supply. The Ammunition Boxes in the F-N.4 were fitted in the Turret under the Guns, which limited the Supply and affected the Trim of the Aircraft. A new Supply System was devised in which large capacity boxes were fixed to the sides of the Rear Fuselage, the Ammunition Belts being taken from the Boxes along Steel Tracks to the Base of the Turret.

 

[Tigerausfb]

 

F.N.4  - you can see two of the four 1000 round boxes

 

And F.N.4A (no idea what the A was for) and the other two cans

 

 

Andrew

Edited April 19 by Tigerausfb

[Jure Miljevic]

Hello,

I am not sure about it. So far I have not seen any Manchester photos with FN.20 turrets. Lancaster prototype, converted standard production Manchester I BT308, clearly had FN.4 tail turret (photo found here)

 

Perhaps some kind of mix-up or typo? Cheers

Jure

[Geoffrey Sinclair]

For a small production run the Manchester can be quite complicated.  The serial registers and contract cards note L7297, L7285, L7289 and L7293 will be the 97th, 98th, 99th and 100th official production aircraft respectively, despite being the twenty second, tenth, fourteenth and eighteenth serial numbers of the order, all counted in the contract cards as produced in July 1941.  They had been diverted onto a new contract for armament development work.

 

Robert Kirby in his book the Avro Manchester (second edition) states the first twenty Manchester had the triple fin twenty eight foot span tailplane, then came the triple fin thirty three foot span tailplane, both these types were considered mark I, while only the last twenty seven Avro produced Manchester were built as mark Ia with the twin fin thirty three foot span tailplane, that is L7583 to L7497 and L7515 to L7526.  Many mark I were converted to Ia.  The book notes the FN.4 was to be fitted to the first batch, the FN.20 to all later production, then came changes to the FN.20 design, a circular cupola that was later abandoned, delaying things.  The first Manchester order was for 200, what constitutes the first batch in unclear, but https://www.rafmuseum.org.uk/documents/Research/RAF-Historical-Society-Journals/Journal-55.pdf page 108 says as of December 1939 it was the first 50 aircraft, in the end both this order and the one for 100 from Metropolitan Vickers were a mixture of Manchester and Lancaster.  Avro built 10 Manchester and the first 2 Lancaster in October 1941, then 1 Manchester and 3 Lancaster in November, thereafter Lancaster, Metropolitan Vickers built 5 Manchester and its first (1) Lancaster in January 1942, then 5 Manchester and 2 Lancaster in February, then 1 Manchester and 1 Lancaster in March, thereafter Lancaster.

 

Early FN.4 Manchester installation was unsatisfactory and needed modifications including a 6 inch extension to the fuselage.  The RAF Performance Chart says 1,000 rounds per machine gun carried plus a 2,000 round reserve.  It does not seem to have been much trouble to change the rear turret from FN.4 to FN.20.  The FN.4 were also fitted to Whitley and Stirling.

 

Anyone near the British Archives might check: AIR 2/4928 AIRCRAFT: Armament (Code B, 5/15): Fraser Nash gun turrets: advance information Date: 1942-1945 and AVIA 46/117 A.V. Roe Manchester Date: 1936-1944, which is a biography of the type.

There is book British Aircraft Armament Volume 1: RAF Gun Turrets from 1914 to the Present Day

 

Avro serials, 50 L7276-L7325, 30 L7373-L7402, 20 L7415-L7434, 45 L7453-L7497, 12 L7515-L7526
Metropolitan Vickers serials, 30 R5768-R5797, 13 R5829-R5841

 

L2780 AMDP at Avro 4 August 1940, trial installation of FN.20 turret, which was over 3 months before it was delivered.

 

It should also be noted that each Manchester required two Vulture engines and the cumulative total of the number of officially produced Manchester exceeds twice the cumulative total of Vulture engines Rolls Royce says it produced during the period August to November 1941, with the maximum difference being a shortage of twenty nine engines in October.  Indicating a number of Manchester (probably R5769 to R5841 from Metropolitan Vickers but assembled by Avro) must have been officially produced either without engines or had them removed shortly afterwards.  Cumulative totals to the end of 1941 were one hundred and eighty eight Manchester versus around four hundred and ten production Vulture engines, including all six Vulture mark V, the rest were the standard mark II.

[Graham Boak]

My understanding is that the Sunderland also had some version of the FN4, as did some marks of Whitley?

 

More relevant to this thread is just where the reserve ammunition was carried, and how this was put into use?  It would seem to solve the problem of the photo showing internal ammunition tracks and the claim that all ammunition was inside the turret.

[Duggy]

An air gunner, in the Nash and Thompson FN4A tail turret of an Avro Manchester Mark I of No. 207 Squadron RAF, trains his four .303 Browning machine guns on the photographer at Waddington, Lincolnshire.

(IWM photo)

From here -- http://axis-and-allies-paintworks.com/e107_plugins/forum/forum_viewtopic.php?p=1&id=413#post-413

Edited April 20 by Duggy

[Selwyn]

2 hours ago, Graham Boak said:

My understanding is that the Sunderland also had some version of the FN4, as did some marks of Whitley?

 

More relevant to this thread is just where the reserve ammunition was carried, and how this was put into use?  It would seem to solve the problem of the photo showing internal ammunition tracks and the claim that all ammunition was inside the turret.

Its not a claim that the ammunition was in the FN4 turret, it was a fact. I very much doubt that there was any reserve ammunition for the FN4. The prospect of pulling out and replacing  heavy ammunition tanks over Germany in the dark,would have been daunting at best.  Have you any idea how heavy 1000+ rounds of .303 weighs? and that would be only  one box not four. And of course it would leave the aircraft very vulnerable at that point of changeover at the worst time.

The FN4 was also used on the Stirling, Along with the other installations you mentioned. The FN 4 was a good turret and well liked but not perfect. The experience gained on ops was reported by sqn gunnery leaders. who identified the deficiencies of the FN4 such as the limited ammunition supply, and lack of armour, that led to the updated FN20 The main point of the updated FN20 was that the ammunition was held remotely and fed on long tracks which basically tripled the available ammunition supply.

[Selwyn]

18 hours ago, Jure Miljevic said:

Hello,

I am not sure about it. So far I have not seen any Manchester photos with FN.20 turrets. Lancaster prototype, converted standard production Manchester I BT308, clearly had FN.4 tail turret (photo found here)

 

Perhaps some kind of mix-up or typo? Cheers

Jure

How can you tell, externally they are pretty much the same thing?

[Graham Boak]

I meant to say "only" rather than denying what had been demonstrated, but your comments on the problems of manually resetting make them clear.  Any engineering solution seems difficult to provide.

 

The FN20 is narrower, flatter sided and less curved in side view.

 

There still seems to be no comments linking the actual serials of Manchesters with each turret, which could support or deny the position of the changeover in  production. 

[Selwyn]

9 minutes ago, Graham Boak said:

I meant to say "only" rather than denying what had been demonstrated, but your comments on the problems of manually resetting make them clear.  Any engineering solution seems difficult to provide.

 

The FN20 is narrower, flatter sided and less curved in side view.

 

There still seems to be no comments linking the actual serials of Manchesters with each turret, which could support or deny the position of the changeover in  production. 

I agree. There is a picture of an FN 20 fitted to a Manchester prototype  but obviously this does not prove that the were Fitted to Manchesters.

an interesting watch by the way.

FN4 turret restoration

 

The FN 20 was very flat sided too

 

FN 20 demonstration

[Walter Lindekens]

Actually, it is fairly easy to identify the FN4A.    Unlike the FN20, which seems to have had a standardized cupola design, the FN4A came with specific cupolas for each of the types it equipped.     Here are some snips out of AP 1659A - Vol I:

 

 

The Whitley version has very straight sides and a large perspex side panel.   The Stirling version, also fairly straight sided, has a diagonal bracing bar.   The Manchester version, alltogether more "bulbous" in shape, with sloping sides, has a horizontal bracing bar midways the side panel. 

 

I have yet to see a photo of a Manchester with an FN20...

 

As stated above, the FN4A had an internal ammunition supply of 1000 rounds per gun, and could not be fed from ammunition boxes inside the fuselage, unlike its successor the FN20.   So why are we seeing fuselage ammo boxes and tracks going to the aircraft's tail in the Manchester photos shared by Selwyn?    I had a quick look in AP 1600A Vol I, which covers the Manchester and there I found:

 

"A rotating gun turret (type F.N.4) is provided at the rear end of the fuselage.   For operation of the turret see A.P.1659A, Vol.I.     The spare ammunition for this turret is supplied by means of ducts from the boxes on each side of the fuselage at the rear end of the main floor."

 

Seems that the idea was for the rear gunner to pull a length of ammo belt out of the tracks and then load it in the turret boxes.    Extremely unpractical to ask that of a gunner in a cramped turret, in bulky flying clothing!

 

The "A" suffix, by the way, denotes a turret for landplane use,  "B"suffix denotes flying boat use.    The FN4B was used on the Saro Lerwick and the Short Sunderland.     Main difference was that "A" turrets were plumbed for oxygen supply, "B" turrets weren't.

 

Cheers,

Walter

[dogsbody]

Great videos, Selwyn!

I really need to get back down to the Bomber Command Museum, at Nanton. It's just such a long drive down there. Just over 800 km.

 

 

 

Chris

[Finn]

Here is some details of the FN.20 turret:

 

 

Jari

[593jones]

Just to muddy the waters regarding ammunition supply to the turrets, John Bushby, an air-gunner who served on 83 Squadron, initially on Manchesters before the squadron converted to Lancasters, wrote in his memoirs:

 

"It transpired that someone in authority had decided that the current design of separate ammunition tanks for each gun limited the amount of rounds which could be carried.  This was true, in a sense, since a tank held a maximum of a thousand rounds.  Nevertheless none of us had felt up until then that an aircraft total of eight thousand rounds was inadequate.  It all depended where they were aimed.  Of course, the more ammunition one had, the merrier one could fire: but since in night combats there was rarely time for more than one or two bursts, it was generally h eld to be quite sufficient.  However, a desk-borne theorist had decided otherwise and within the van was the answer.  Since the ammunition tanks located in the rear turret could not be enlarged, for the very good reason that there just wasn't room enough to do so, henceforth these would be removed and replaced by larger tanks, holding three thousand rounds per gun and positioned in the fuselage about half-way down.  Long rails would then lead the ammunition belt down to the rear turret and up to the guns.  We immediately thought of several snags, each brushed aside by the firm's representative.

"What happens when  you rotate the turret?  Won't the belts get twisted?"

Here he went into a long explanation of a special swivelling feed device wh;ch his firm had developed.  This had been tested until etc., etc.

"What happens if the rails get damaged?  Surely that will stop the belt and therefore the gun?"

"Oh, you'll just have to be careful they don't.!

I thought of the flight mechanics, struggling to their inspections and checks in a confined space and size ten boots and wondered.

Not long after, all our Lancasters were modified with this new arrangement and it became a chargeable offence to put a foot anywhere near these ammunition rails.  In the event the damned things never did work properly in my experience and cases of belts jamming through a slight dent in the guide rails became commonplace."

 

John Bushby Gunners Moon Ian Allen 1972

 

It would seem from that, that, initially, at least, Lancasters had rear turrets with a self contained ammunition supply.  Presumably they were not the FN4, so did the FN20 initially have the ammunition tanks as did the FN4?

[Graham Boak]

Or is Bushby actually talking about the Manchesters he served on?  It is worth adding that such rails were used on all subsequent aircraft throughout the war and later without (it seems) any great outcry to improve them.  But then possibly the ground crew/production line became better at installing them.  Problems are common with initial issue of pretty well any piece of kit.

[Finn]

A view of the inside of the turret:

 

 

edit: a brief view from a video:

 

Jari

 

Edited April 22 by Finn

[593jones]

14 hours ago, Graham Boak said:

Or is Bushby actually talking about the Manchesters he served on?  It is worth adding that such rails were used on all subsequent aircraft throughout the war and later without (it seems) any great outcry to improve them.  But then possibly the ground crew/production line became better at installing them.  Problems are common with initial issue of pretty well any piece of kit.

 

That was my first thought when I first read it, but Bushby does say that they were equipped with Lancasters at the time 'Not long after, all our Lancasters were modified with this new arrangement'  Of course, Bushby was writing some thirty years after the events he was describing, so it is possible his memory was at fault.

[Graham Boak]

I think we need photos of very early Lancasters before ruling that early ones had FN 4s.  That late Manchesters had FN 20s suggest that any overlap of the earlier one into Lancaster production would be small - if the FN 20 was fitted to a significant number of Manchesters then finding any on Lancasters would be most odd.  Prototypes and early test aircraft perhaps excepted?

[Graham Boak]

There are pictures of very late Manchesters in the Wingleader book showing the FN4A turret.    I couldn't find any pictures or refence to the FN20 in this or the Kirby book (but it was a pretty quick flick through).  I shall leave it to others to find Lancasters with the FN4A.

[SafetyDad]

On 23/04/2025 at 15:13, Graham Boak said:

I think we need photos of very early Lancasters before ruling that early ones had FN 4s.  That late Manchesters had FN 20s suggest that any overlap of the earlier one into Lancaster production would be small - if the FN 20 was fitted to a significant number of Manchesters then finding any on Lancasters would be most odd.  Prototypes and early test aircraft perhaps excepted?

 

According to the Wingleader book on early Lancasters (No 5), it seems that even the Lancaster prototypes had FN20 rear turrets, as did all of the early production examples. No FN4s that I could see.

 

HTH

 

SD