PZL P.23 Karas (crucian carp) was developed in the early 1930s in response to the Polish Air Force's need to replace its ageing biplane Potez 25 and Potez 27 light bomber/reconnaissance aircraft. The specification presented to PZL in 1931 (Panstwowe Zaklady Lotnicze - the State Aviation Works) called for an all-metal light bomber plane powered by a Bristol Pegasus air-cooled radial engine, which should carry a minimum 600 kg (1330 lb) bomb-load, and whose maximum speed should reach 300 km/h (186 mph). Another requirement was the ability to operate from improvised airfields. It was soon decided that the new plane's design would be based on the PZL 13 fast passenger/transport airplane project by Stanislaw Prauss, which had been abandoned in early 1931. 
 

The first PZL P.23 prototype

Necessary changes to the project, apart from fuselage redesign, included the addition of wing flaps, and the provision for weapons mountings. The wing was designed by Franciszek Misztal, based on his original stressed-skin main spar concept, which had earlier been only tested on the PZL 19 high-performance touring airplane. Serious problems with the wing's construction caused delays, and the first prototype, powered by the Bristol Pegasus II M2 engine made its maiden flight in August 1934.

The first prototype revealed many problems, which were overcome by the second and third prototypes. The fuselage was redesigned, with internal bomb bay removed to provide more space for the crew, and engine installation lowered for better visibility. The wing's mechanization was redesigned with automatic slats added on the leading edge, and the wing root fairings significantly enlarged. After additional changes to the engine fairing and the exhaust, the airplane was accepted by the Lotnictwo Wojskowe and given the designation PZL P.23A Karas. An order for 200 aircraft was placed with the PZL. 
 

PZL P.23B at Cracow Rakowice airfield, spring 1939

The production started in the end of 1935 but its pace suffered because of frequent problems with the Pegasus II M2 engines, license-built by the Polish Skoda works (this engine variant was never produced by Bristol). In addition, the leading-edge slats proved unreliable, and were consequently removed. Only 40 P.23As were built and assigned to training duties, pending the availability of the P.23B variant fitted with the more powerful Bristol Pegasus VIII engine, whose production commenced in the summer of 1936. In February 1937 the production reached the pace of 20 aircraft per month, and the original order for 200 P.23s was fulfilled in September 1937. Additional 50 aircraft were ordered, and the production of the P.23B variant concluded in February 1938.

Meanwhile, an effort was being made to adapt the P.23 for the dive-bombing role, which resulted in a prototype designated PZL P.42. Although the plane's dive-bombing capabilities proved poor, it became the basis for the more successful PZL 46 Sum horizontal bomber which was supposed to replace P.23s in first-line units starting form March 1940.
 

One of the first P.43s at Warsaw's Okecie airfield

In early 1936 Bulgaria placed an order for 12 P.23s, with the additional requirement of a more powerful engine and an additional forward-firing machine gun. The fuselage was thus redesigned to accept the Gnome-Rhone 14N-01 engine, and the plane was given the designation PZL 43A Tchaika (sea gull in Bulgarian). Because of delays in engine shipments from France, this first series was eventually fitted with Gnome-Rhone 14kfs engines, while additional 42 planes ordered by Bulgaria, designated PZL 43B, received the intended GR 14N-01 engine. At the outbreak of war nine of these aircraft were still at the Warsaw Okecie airfield, and five of them saw combat in the Polish Campaign.
 

A crashed P.23 of 41 Eskadra being examined by German soldiers, September 1939

During the September campaign 114 P.23s were flown by first-line units, and additional 11 (including the five PZL 43s) were received as replacements. Of these, only 17 reached Romania on September 17. Such a high attrition rate was caused in most part by the inability to repair the aircraft, so a large proportion of the planes was abandoned after receiving combat damage. Still, used for attacks on heavily defended German motorized and Panzer columns, flying without fighter escort, many planes were lost in combat.
 

Romanian P.23s on the eastern front, summer 1941

After the collapse of Poland, about 30 P.23s from both first-line and training units reached Romania. After receiving a major overhaul, 19 of these aircraft were impressed for local service, and saw combat on the eastern front, flying reconnaissance and bombing missions over the Crimea and Don river, and were withdrawn from the front in January 1943, following the collapse of the Axis troops at Stalingrad. From the summer of 1943 the remaining Romanian P.23s were relegated to training duties.

The PZL 43 equipped units of the Bulgarian air force never saw front line combat, and were used locally against communist guerillas throughout 1943 and 1944. In September 1944, after Bulgaria switched sides and joined the Allies, the Tchaikas were finally replaced by aircraft of indigenous design.