When did 100 Octane fuel become generally available?

My sources say that the RAF were using 100 Octane fuel in the Merlin engines of Spitfires and Hurricanes from the Spring of 1940. Does anyone have any information that’s a bit more specific?

Whilst creating my 11 Group Fighter Airfields spawn point maps I’m going to add the 100 Octane variants from Aug onwards. Do you think this is realistic or should they be available earlier or later?

Cheers for any insights.


Yep, Spring 1940.
Will look in my massive Spitfire book for any more details.


Cheers Splash,

While you’re at it, what the difference between the Spitfire Mk1 and the Mk1a. Did the ‘a’ get introduced purely to differentiate it from the cannon armed ‘b’?


what the difference between the Spitfire Mk1 and the Mk1a. Did the ‘a’ get introduced purely to differentiate it from the cannon armed ‘b’?


Yep. Ia = 8 x .303 Brownings, Ib = Cannon armed (usually 2 cannon)

In CoD the major difference between the Spitfire 1 and 1a appears to be the propellor. The Spit 1 may have a two pitch propellor, with a constant speed prop in the Spitfire 1a (need to check in game).

Historically the de Havilland (pointy) propellor came first*, with the Rotol (rounded) following later.
De Havilland issued a conversion kit (from June 1940) to make their two pitch propellor into a constant speed unit - Rotol were always constant speed.

There shouldn’t be a major performance difference between the two constant speed units - both propellor types seem to have been used on Mks I, II and V Spitfires.

*I’m ignoring the pre-war Watts (fixed pitch, two blade) propellor

Whiskey here you go, bit of background for you.

100 Octane developed when chemists (America) were endeavouring to increase the anti-knock (pre-ignition) qualities of petrol.
It was extremely expensive but despite high costs the US Army Air Corps were using it in its aircraft in late 1939.
The RAF got involved with 100 Octane in the Summer of 1935 when on the 29th July it was decided that 95 or 100 would be in general use in two or three years time.
Samples of both 95 and 100 Octane fuel was received from America and the Asiatic Petroleum Company offered 90 octane in quantity in 1936 at a rate of 15M gallons per annum. Shell Mex and Anglo American offered the same quantities the following month.
By 2nd November 1937 three RAF Squadrons were using 100 octane in their aircraft.
A meeting was held on the 16th March 1939 to consider the question on when the 100 octane fuel should be introduced into general use for all RAF aircraft, and what squadrons, number and type, were to be supplied.
The decision taken was an initial delivery to sixteen fighter and two twin engined bomber squadrons by Sept 1940.
First trial in a Spitfire took place at Rolls Royce, Hucknall on 24th Sept 1939 when K9788 fitted with a Merlin RM3S (XII)suitably modified to burn the fuel. The result was take off decreased by 30 yards and improved performance at all altitudes.

This was all before war loomed on the horizon, as war broke the dates were brought forward to get into service as soon as possible.
The combination of the CS (Constant speed) propeller and 100 octane fuel put the British fighters on a par with the Luftwaffe.