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A light mist wafted over England on the morning of Sunday, 15 September
1940. The haze lifted to reveal a beautiful day marred only by patchy clouds.
Winston Churchill drove to the RAF base at Uxbridge, west of London. The
day looked good for flying – and he wanted to watch an air battle.

This was the best place in the whole of Britain to witness a Luftwaffe
raid because Uxbridge was the home of No 11 Group of Fighter Command. This
group provided air defence for London and southeast England and had borne
the brunt of the two-month-long Battle of Britain. Air Vice-Marshal Keith
Park was presiding over the defences from a bunker complex 60 feet below
ground the day of Churchill’s visit.

Two narrow flights of stairs led to the subterranean operations room.
‘I don’t know whether anything will happen today,’ Park said as the men
descended. ‘At present all is quiet.’

At the bottom, a long corridor led to the plotting room. There, like
casino croupiers, airmen and members of the Women’s Auxiliary Air Force
kept tabs on British and German aircraft by pushing wooden markers around
a gigantic map.

CHURCHILL’S OVERVIEW

Churchill took a second corridor that led up to a bank of three viewing
cabins. He seated himself in the centre cabin. On the opposite wall a vast
totalisator, or tote board, glowed with a bewildering array of coloured
lights and numbers.

The plotting map and tote board formed the hub of a tight-knit aircraft
detection scheme. During the war, a radar network protected the east and
south coasts. Radar reports were correlated and tabulated by position, altitude
and bearing at Fighter Command headquarters in nearby Stanmore. Landlines
and teleprinters transmitted this information to Park’s operation room,
where plotters listened on headphones. Simultaneously, loudspeakers broadcast
details of which squadrons the controller had decided to scramble to meet
an attack.

On the map, RAF units were represented by triangular wooden blocks.
Numerals slipped into tracks on their sides revealed the planes’ altitude
in thousands of feet – and the number of angels, or friendly fighters, in
the formation. Discs represented German planes, showing a code number and
the attack size: ’30+’ or ’40+’.

The tote board provided all the relevant operational details needed
by the controller – latest weather, height of the balloon barrage layer
guarding key cities, and whether the British fighters were in the air, on
the ground, or needed refuelling. The country was divided into sectors,
each of which controlled several airfields.

In a rapidly shifting air battle, controllers needed to know how up-to-date
their information was. The key lay in stacks of four electric bars – white,
blue, yellow, and red – linked to a special clock mounted on the wall under
the totalisator. The outer edge of every five-minute section on the clock
face had been painted alternately in red, yellow, or blue. Whenever information
on a squadron was updated, switchboard operators illuminated one of the
bars. The colour matched the section containing the clock’s minute hand
when the news came through. A glowing white bar signified news more than
ten minutes old: that rendered it unreliable.

Adept at reading the tote board’s shifting numbers and colours, controllers
barked orders by telephone which were relayed to pilots by radio.

Around 11 am, not long after Churchill arrived, the plotters in the
operation room began stirring. Radar showed massive formations of enemy
aircraft over Calais and Boulogne. Soon the attack’s growing size and scale
jumped off the German markers: ’20+’, ’40+’, ’80+’. In concert, the tote
board’s pattern of glowing bulbs began to change.

The attacks kept coming. Park strode up and down the cabin, reinforcing
some areas, moving fighters to defend new zones. Before long, the tote board
showed every squadron committed, and over a red-hot line to Fighter Command
head-quarters Park tried to round up three reserve squadrons.

‘What other reserves have we?’ the prime minister asked. ‘There are
none,’ Park shot back. Churchill looked grave. ‘The odds were great; our
margins small; the stakes infinite,’ he wrote later. Within minutes, though,
the German attack broke off. The next morning’s Daily Herald screamed: ‘175
Nazi Planes Down, RAF Triumphs in Biggest Air Battles of War.’

Subsequent analysis put actual German losses at 60. Nevertheless, the
tally exceeded any day’s except 18 August, and dwarfed RAF losses of 26.
More critically, Hitler had been categorically denied the daylight air supremacy
he needed to storm the country. Two days later, the Fuhrer postponed his
invasion plans indefinitely.

The underground operations room has been preserved to show how it appeared
during the battles of the morning of 15 September 1940. Individuals and
groups can tour the complex, but only by arrangement. Write to: Warrant
Officer Chris Wren, RAF Uxbridge, Middlesex. Tel: 0895 237144.

Robert Buderi is a freelance writer based in Cambridge, Massachusetts.