[Laurent Rizzotti]

Not exactly. At the start of the war the usual formation for French fighters was a 3-plane formation (called patrouille). These 3-plane formations could be combined to form 6 (2 * 3) or 9 (3 * 3) formation, respectively called "patrouille double" et "patrouille triple".

Bigger formations were usually described as combinations of the above, with for example a "patrouille triple" with a "patrouille double" as high cover, for a formation of 15 aircraft.

The patrouille légère was the name given to the formation with only 2 aircraft. As for the usual "patrouille", it was possible to combine them and form a "patrouille légère double" with 4 aircraft (2 * 2). AFAIK, there was no "patrouille légère triple" used, as the 6 aircraft will rather fly in two formations of 3 ("patrouille double").

The French équivalent of the Observer Corps in 1939-1940 was the "service de guet aérien" or "guet aérien".

Subunit: there is no such size distinction in France.