Now that Tamiya have released a new-tool Spitfire Mk.I this article is out of date.  We leave it here for those who still wish to build the old version of this kit.
Josip
Tamiya Spitfire (Mk.I) questions…

Wed Jul 30 11:28:11 2003
Finally got my long time desired 1:48 kit of Spitfire from Tamiya. My plan is to build this one+109E as a BoB display.
I find it to be a jewel but as always there are some issues…
There is no armour plate. Is this correct?
Which canopy to choose, the one with a port side window (why was this fitted) or the clean one?
Which is the colour of double oxygen bottle, interior green or silver?
Should black undersides be limited only to port wing or the whole left half of the aircraft?
What to use for mg covers?
And finally should the seat be painted green with black padding as per instructions or that reddish brown Bakelite colour?

Bob Swaddling
Battle of Britain Spitfire

Wed Jul 30 13:14:47 2003
Hi Josip
The BoB ran from July through to October 1940. A lot depends on which Spitfire you want to depict. Generally:
1.Armour plate was installed
2.Sliding canopy with the clear vision “knock-out” panel on the port side. Remember that this is just an oval of Perspex over an oval opening in the hood and held on with six Perspex rivets, so don’t paint the frame at all around it as there was no frame there. It was intended for clear vision if the canopy frosted up. Pilots did knock it out to release pressure in a screaming dive trying to get out but that was not the intent of the panel.
3.The double “oxygen” bottle isn’t an oxygen bottle. It is compressed air bottles and they were steel coloured.
4.Paint the underside “Sky Type S”. Black & White were long gone by the BoB. The wheel wells, oleo legs and fairings, and even the wheels were the same colour, same for the tailwheel.
5.The Tamiya Mk I comes with the muzzle flash eliminators extending past the leading edge of the wing. These were for night fighting which was not one of the Spitfires strong points. They were removed early in the war. They must be removed from the Tamiya wing too. The m/g blast tubes were covered with a dull red tape best depicted in scale by dull red decal cut into squares and put over the blast tubes.
6.Very early Spits had an aluminum seat but BoB Spits had Bakelite seats with a black leather back pad. Bakelite is a reddish brown. I use model Railroad Boxcar red for mine.
These are just general answers for BoB Spits and there are always some differences. That is where photo reference comes into play. One tip on the Tamiya Mk I, if you are doing DW-O as in the kit markings, apply the fin flash backwards (with the blue forward) as the actual a/c had it that way seen in period photos.

Graham Boak
BoB undersides

Wed Jul 30 13:04:53 2003
Jonathan is right – the various permutations of partial black/white undersides were not carried during the Battle itself. The correct undersurface colour was Sky. However, this was not available in the quantities required so substitutes were initially used by some units. These included Sky Blue, Sky Grey, and Eau-de-Nil. The best description of these possibilities is in the Scale Aircraft Modelling booklet about the Battle of Britain, by Paul Lucas.
If you know which a/c you wish to model, better advice can be provided.

Don Flynn
Basically what Jim said, and on the mg port covers…..

Wed Jul 30 12:18:06 2003
I would either use red decal film or Tamiya tape painted red if it was me, I’ve also seen people use red crepe paper but never had any luck with it.

Jim Penhale; Model Citizen
A few attempts at answers! 

Wed Jul 30 11:55:32 2003
First off, by the time the Battle of Britain rolled around d most aircraft were fitted with armour plate, so that should probably be added.
You’ll have to pick the canopy yourself based on photos. The one with the panel on the side could be in use during the BoB. The clear panel was designed to be punched out by the pilot to equalize the pressure inside and outside the canopy if he had to bail out. It was felt that this pressure differential (due to airflow at high speeds) might prevent the pilot from getting out. It was found not to be an issue so was discontinued.
Oxygen bottles were probably silver or white.
Undersides could be, at various times of the BoB; aluminum lacquer, black and white, sky, or another colour called “duck egg blue”. You’ll need pictures to figure out which you want to do. If you’re doing the black and white it could be either the entire aircraft or just the wing. Also, some planes apparently had the ailerons black on the white side and white on the black side!
I’m not sure what you mean by machine gun covers? One thing to note is that by the time things really were heating up the barrels did NOT protrude from the leading edge of the wing as shown in the kit. You’ll need to go to the photos again, and maybe trim those back.
Seat should be Bakelite, although I seem to recall somewhere that very early Spitfires had a green painted aluminum skin on the seat. I’ve not been able to really confirm that to my satisfaction, though.

Brad
I seem to recall chatting with Bob Swaddling

Wed Jul 30 13:00:19 2003
Hi Jim,
He felt that some units in the field were making the armour plating to some of the planes that didn’t have it, both head and seat armour. Also, he did stress big time to me that the punch out portion of the glass in the hood/canopy, shouldn’t be painted, i.e.: there was not framing there to paint.

Josip
I meant those red patches (of ?)

Wed Jul 30 12:25:03 2003
that were put over the busy end of MG barrels to prevent the cold and dirt. What is the best thing to use in 1:48?

Jonathan Strickland
BoB Spits

Wed Jul 30 11:42:00 2003
It will help to know which Spitfire you plane to do and from which date. Markings changed several times in 1940, but generally speaking Spitfires did have armour plating behind the (Bakelite colored) seat by the Battle of Britain. However, the undersides were one colour from (end of) June 1940 until November, which is considered the span of the Battle (July 10 to the end of Oct, actually).
If you decide to do an actual BoB Spit the real question is underside roundels or none. These added after the Battle started.
So, again, pick a specific Spitfire (maybe one that has been documented a little) from a specific date and that will help clear up some of your markings questions.
As to airframe questions, I leave that to the boffins.

Jim Penhale; Model Citizen
Wed Jul 30 14:02:38 2003
Hey Bob,
I was interested in your comments regarding the clear panel on the canopy. I’ll probably live to regret this, but I’m going to disagree on this matter of Spitfire minutiae with you! (living on the edge, I guess!)
I know I read somewhere that that was the case (the pressure thing) which makes sense to me. After all, if it were for frosted canopies, why did they discontinue it, and what good would it do on the side? Why not just slide back the canopy?
Time for me to hit the books and see what I can come up with!

source: Hyperscale
(thanks to Brett Green for permission)