The twin brothers Walter and Willi Gabriel were born in 1893 in Bromberg in the Prussian Provinz Posen. They took an early interest in aviation and 1910-1912 in Bromberg they built four gliders (later called P I, P II, P III and P IV in Poland). Then they built monoplane on the lines of the Fokker Spinne, which flew in Bromberg in 1912-1913. Willi Gabriel was the leading one of the two.

During World War I both served in the Air Force as pilots. Walter on two-seaters, and Willi as a fighter pilot. Willi Gabriel served in Jasta 11, became an ace with 11 victories, and came in conflict with Hermann Goering.

After World War I the brothers resettled in Bromberg, which by now had become part of the new Poland, and was called Bydgoszcz. They took over the furniture factory of their father, and under the new political circumstances they took Polish first names, Walter became Paweł, and Willi became Jan (about this change of first names, see Samoloty w Lotnictwie Polskim, http:/www.samolotypolskie.pl/samoloty/1067/126/Gabriel-Walter-Pawel).

In Bydgoszcz the Gabriel brothers continued their interest in aviation, and in 1923-1925 they built some light planes.

German and Polish sources give different designations for the Gabriel projects:
- The designations P I to P IV are found only in Polish publications.
- The 1912 monoplane apparently had no designation, neither in German nor in Polish publications.
- The Polish P V is the German P 5.
- The Polish P VI is the German G 6E, and the P VII the G 6D. The P VIII is simply a variant of the G 6 series.
- The Polish P IX is the German L 7a.

Being Germans, even if they took Polish first names, in 1926 the Polish authorities forbade them further aviation activities.
The Gabriel brothers then settled in Berlin-Johannisthal, where in 1928-1929 they built a last sporting biplane, the G 8 Wespe.
Willi Gabriel died in 1968.

Sources:
- Lange, Typenhandbuch der deutschen Luftfahrttechnik (1986)
- Glass, Polskie konstrukcje lotnicze 1893-1939 (1977)
- Glass, Polskie konstrukcje lotnicze do 1939 - Tom 1 (2004)
- Cynk, Polih Aircraft 1893-1939 (1971)