The Inter-War years
With the end of the war the company rapidly diversified, using their factories to produce chassis and engines for the Rolland-Pilain and Piccard-Pictet cars, along with Ansaldo diesel engines, refrigerators, sewing machines and even jackhammers. In 1920 they also introduced their first motorcycle, simply known as the Gnome et Rhône 500 cc. Various models were produced up to the early 1950s, typically advertised as simply "Gnome Rhone" with no accents.
By 1920 their rotary engines were no longer competitive, and they had no new designs of their own. In 1921 they took out a license for the Bristol Jupiter, which was in the process of becoming the Gnome of its era. In 1922, Paul-Louis Weiller, a World War I ace, took over the company and decided to focus it on aircraft engines once again. Their Jupiter designs, the 9A, were soon selling very well. In 1926 they took out a license for the smaller 5-cylinder Bristol Titan, while Bristol licensed the Farman-style reduction gearing used by Gnome.
Not satisfied to simply produce Bristol designs under license, Gnome started a major design effort based around the mechanicals of the Titan. The results were introduced in 1927 as the K-series, spanning the 260 hp (190 kW) Gnome-Rhône 5K Titan, the 7-cylinder 370 hp (270 kW) version, the Gnome-Rhône 7K Titan Major, and the 9-cylinder 550 hp (405 kW) Gnome-Rhône 9K Mistral. All of these engines were delivered in a variety of improved versions, named with a three letter code; the first letter was the series number (a through f for instance), the second a r or l depending on which direction the engine turned, and the third indicating the charging system. With the introduction of the K-series, Gnome ended royalty payments to Bristol. By 1930 they had delivered 6,000 Jupiters, Mistrals and Titans, making them the largest engine company in France.
But the 550 hp (405 kW) Mistral was no longer powerful enough for the rapidly evolving industry. To provide more power Gnome once again turned to the two-row solution, using two banks of 7 cylinders, delivering the 625 hp (460 kW) Gnome-Rhône 14K Mistral Major in 1929. The new engine was an instant hit. By 1933 the 14Kfrs had improved the power to 1,025 hp (750 kW) through better supercharging (along with similar improvements in the Mistral, now at 770 hp or 570 kW), and the engine was once again being licensed around the world.
Leaving the idea of having many engines in a single "K-series", Gnome continued work with the basic mechanical design to produce the 18-cylinder two-row Gnome-Rhône 18L of 1400 hp (1030 kW). Its power-to-weight ratio was not very good and work on the design was eventually stopped in 1939. A smaller engine, the Gnome-Rhône 14M Mars was introduced to replace the earlier K-series Mistral, notable primarily for its extremely compact frontal area, giving by far the most power for size of any engine of the era. It was especially used in the Potez 631 aircraft family.
In 1936 the 14K-series was replaced by the Gnome-Rhône 14N delivering 1,100 hp (810 kW) from a slightly heavier engine that nevertheless had a much better power-to-weight ratio. Starting with the N they introduced a new naming scheme, replacing the earlier model letters with numbers, delivering the engine in versions that turned left with even numbers and right with odd. The original 14N-0/1 was run through a number of versions, the 14N-10/11 being used on the Bloch MB.210 bomber, the 14N-25 on early examples of the MB.152 fighter, and the 14N-49 on late MB.152s as well as LeO 451s and Amiot 351s. The N-series finally ended with the 14N-50/51, which delivered 1,210 hp (890 kW) for takeoff. The 14N was not as widely licensed, as the war was approaching and the French government was becoming increasingly wary of licensing designs to potential enemies.
The 14N-series was itself replaced by the ultimate pre-war evolution of the line, the Gnome-Rhône 14R. The first versions introduced in 1939, the 14R-4/5, produced 1,291 hp (950 kW) for takeoff and was only slightly heavier than the 14N. By 1940 the improved 14R-8/9 was delivering 1,578 hp (1,161 kW) by increasing RPM from 2,400 to 2,600. Although this was a good figure for the era, British and German design had already passed this mark, and would soon be pressing on 2,000 hp (1,500 kW).
With the fall of France in 1940, Gnome et Rhône was ordered to produce the BMW 801 under license, while the 14M and 14N saw limited use on some German designs, such as the Henschel Hs 129B, Gotha Go 244B, and Messerschmitt Me 323. The company became infamous for slow production, building only 8,500 engines by May 1944, when the Germans had been estimating 25,000. An air raid by 56 Lancasters and 8 Mosquitos of 5 Group of the RAF completely destroyed the original Gennevilliers factories on 9/10 May. Another air raid by Lancasters of 617 Squadron led by Wing Commander Leonard Cheshire had also severely damaged the Limoges factory on 8/9 February 1944.
With the end of the war, the company was in no condition to continue in the aero-engine business, although they picked up small contracts to produce M4 Sherman tanks for the French army. In order to save what was left the company was nationalized on 29 May 1945, creating the Société Nationale d'Etude et de Construction de Moteurs d'Aviation (SNECMA), and producing the 14N, 14R and the new 14U.
