The PZL P.11 was a high-wing monoplane fighter design emerging from Polish aero industry during the interwar years. PZL ("Panstwowe Zaklady Lotnicze") managed nearly all of the primary aviation developments for the country in the pre-World War 2 years and served as its largest aircraft manufacturer. A total of 325 P.11 aircraft were eventually produced up to the time of the German invasion of Poland. The aircraft was used in the ultimately failed defense of the country as the Germans and Soviets claimed the victory. Nevertheless, the P.11 proved a handful for German pilots at times, claiming at least 100 enemy aircraft in the assault.
As with other aircraft of the early 1930s, the P.11 was something of a throwback to an earlier period of flight - its cockpit was open-air and its undercarriage fixed. An aerodynamically refined shape and metal-skinned monoplane wings made it more modern than the fabric-over-wood biplanes of the First World War. However, by the end of the decade, all world powers would eventually evolve to modern fighters featuring all-metal skin, enclosed cockpits, and retractable undercarriages - leaving such designs as the P.11 to the pages of aviation history. Regardless, the P.11 was a sound product of her time and a needed addition to the Polish defensive lines. It handled well, held comparable armament with her peers, and was an agile gunnery platform. Its armament began as 2 x 7.92mm machine guns with 500 rounds afforded to each gun.
The initial prototype was P.11/I and first flight was recorded in August of 1931. This aircraft was powered by a French Gnome-Rhone Jupiter IX ASb engine of 515 horsepower. Then followed prototype P.11/II which fitted a British Bistrol Mercury IV A of 530 horsepower under a revised cowling. The work then led to the P.11/III production prototype which carried the Bristol as its standard installation and featured revisions to her overall design to facilitate mass production at PZL. This third iteration served as the basis for the P.11b which was on order with the Romanian government. The aircraft were powered by Gnome-Rhone 9K Mistral engines of 525 horsepower (or the local Romanian I.A.R. 9K Mistral) and total production numbered fifty aircraft of this mark.
The Polish Air Force ordered the P.11/III was the P.11a and these arrived only after the Romanian order was completed. These showcased Polish Skoda Works Mercury IV.S2 engines and numbered thirty aircraft in all. The improved P.11c mark followed for the Polish Air Force and showcased a more flexible armament suite of 2 or 4 x 7.92mm machine guns.
Romanian local production added the P.11f under the I.A.R. brand label and these were completed with the 9K Mistral engines (595 horsepower) as well as 2 x 7.92mm FN Browning machine guns. The P.11g "Kobuz" was a further Polish variant intended to fill the gap between existing P.11 fighters and the upcoming P.50 Jastrzab ("Hawk") fighters. The fighter carried 4 x 7.92mm KM wz. 36 series machine guns as standard and was powered by a PZL Mercury VIII engine of 840 horsepower in a revised airframe but only existed in prototype form before the German invasion put an end to the promising program's progression.
When the Germans invaded Poland to officially begin World War 2 on September 1st, 1939, the Polish Air Force had on hand a stock of 152 P.11 fighters with 109 of these in serviceable condition. All, save for a few "four-gunners", were armed with twin machine guns and many still awaiting their radio kits. Pressed into service against a determined and veteran foe, the P.11s did not fare well against the more modern German Messerschmitt Bf 109 fighters. A P.11 was the first aircraft to be shot down in World War 2.
While largely outmoded, P.11s held inherent maneuverability over their aggressors and could exact a fair amount of damage in turn when holding the advantage. Rough field operations were also a part of the aircraft's battlefield forte and drove home the rugged and robust qualities of the Polish design. However, its early 1930s heritage eventually betrayed it for losses against its German foes proved heavy though Polish pilots did manage their fair share of kills in P.11s.
By the end of the invasion, combat attrition had lessened the number of available P.11s in service. Poland was eventually split in two by the conquering Germans and Soviets. Some of the remaining Polish P.11 stock was handed to the Romanians for continued service. With their best fighting days behind them, the aircraft line served no more than as trainers or less while being succeeded by more modern mounts.