The 'finger four' is a term for a
formation of
fighter aircraft used by the
RAF during
World War II. It was adopted
after the start of that war, and it was
copied from the opposing
German Luftwaffe's
schwarm formation, which was developed in 1936 and 1937 during
fighting in
Spain. Essentially, in a finger four, two pairs (
rotte in the Luftwaffe) of aircraft operate together; the basic unit pair operates in line
abreast, with one aircraft slightly behind the other. Both pilots concentrate their searches 'across' the formation, so as to cover 'inwards' - this way, the rear aircraft can cover the forward aircraft's tail, and they do not miss the space between them.
The forward pilot concentrates on fighting other aircraft (interception, attack) and the rear aircraft, or wingman, concentrates on protecting the lead pilot from attack. The joining of two pairs of aircraft, with one pair slightly behind the other, and with the two 'lead' airplanes in the center, resembles the spacing of the tips of four fingers when spread out - hence 'finger four.'
Here's an ASCII art representation (or attempt thereof) of the formation:
| -lead aircraft- |
^
=====+===== ^
^ | =====+=====
=====+===== -+- | ^
| -+- =====+=====
-+- |
-+-
| - Pair one - |
| - Pair two - |
The F I N G E R F O U R
(e c h e l o n r i g h t)
Take your right hand and lay it flat, palm down or away from you. The tips of your fingers should approximate the positions of the aircraft. That is a 'finger four,
echelon right.' Using your left hand would make it 'echelon left.'
The aircraft separations would vary. Complete finger fours would take off and land together from RAF bases at times, with separations of twenty to fifty feet (sorry, seven to twelve meters). During flight, it would vary depending on the skill of the pilots, their habits and circumstance, but seems to have averaged some fifty to one hundred feet (fifteen to thirty meters, perhaps) between aircraft. The purpose was to emphasize the link and supporting relationship between airplanes and between pairs, so during combat or expected combat the formations would draw in tighter. Once a dogfight began pairs were supposed to stick together at the very least, although sometimes that wasn't possible.
The introduction of the 'finger four' in RAF tactics is attributed variously. Some sources point to Douglas Bader, some time after his taking command of Tangmere Wing in March 1941. The Wing consisted of three squadrons of Supermarine Spitfire fighters along with a squadron of Beaufighters, with the latter used typically for nightfighting. Other sources cite Sailor Malan and cohorts, a year earlier during the more desperate fights earlier in the Battle of Britain. Although it may never be precisely clear who (if anyone) was a driving actor, it does seem widely acknowledged that the original two-pair formation was used by the Luftwaffe - so all observant RAF pilots and tacticians would have been exposed to it from at least the beginning of hostilities. Some may in fact have observed it during the Spanish Civil War, or taken note of it from reports, although without first-hand experience in combat against it it is unlikely they would have had much pressure on them to adopt it.