At the outbreak of World War II the P.Z.L. P.37 Lot (elk) was not only one of the most advanced bombers produced by the Polish aircraft industry to that date, but was also the only aircraft in service with the Polish air force that could be regarded as being of modern design. P.Z.L. had proposed the P.Z.L.3 advanced bomber to meet a Department of Aeronautics requirement for an aircraft in this class, but the financial stringencies of 1930 prevented the PZ.L.3's progress beyond the design stage. P.Z.L.'s next proposal was for a bomber version of the P.Z.L.30 civil transport which, having failed to attract a buyer, was converted as a bomber prototype by P.Z.L. It was later developed and put into production by the L.W.S. company as the L.W.S.4 Zubr. P.Z.L, then produced the design for a twin-engine bomber of monoplane configuration, gaining a contract for three prototypes in 1935. The first of them, the P.Z.L. P.31/I, was flown initially in late June 1936.

Successful testing of this aircraft, which was powered by two 873 hp (651 kW) Bristol Pegasus XII radial engines, led to a contract for 30 under the designation P.37A Los A. Production was completed in 1938, the first 10 having a single fin and rudder, but the last 20 sporting the twin fins and rudders which had been introduced and tested on the P.37/II prototype. This latter prototype had also been used for development testing of engines in the 1,000 hp (746 kW) class by manufacturers that included Fiat, Gnome-Rhôene and Renault. Demonstrated at an exhibition in Belgrade during 1938 and at the Paris Salon in the same year, the P.37A created enormous interest, resulting in export orders for a total of 35 P.37C bombers powered by 970 hp (723 kW) Gnome-Rhône 14N.07 engines for Bulgaria (15) and Yugoslavia (20), and 40 P.37D bombers with 1,050 hp (783 kW) Gnome-Rhône 14N.20/21 engines for Romania (30) and Turkey (10). In addition, Turkey ordered components for 15 more aircraft and signed a licence to manufacture. Planned delivery for these export aircraft was from June 1940 and as a result, none of them was completed. The delivery of Los A aircraft to the Polish air force began in early 1938, and all of these were equipped subsequently with dual controls for use as conversion trainers.

Delivery of the ensuing P.37B Los B (which introduced a revised cockpit canopy, twin-wheel main landing gear units and Pegasus XX engines) began in late 1938. A total of 150 had been ordered, but policy changes that favoured fighters rather than bombers reduced the number to 100, and only about 70 of these had been delivered by the outbreak of war. Even more disastrous for Poland was the fact that of the Los B aircraft in service only 36 were fully equipped for operational use, though these were supplemented quickly by nine more replacement aircraft. Some 26 of this number were lost in action, and on 17 September 1939 the survivors, plus about 20 other P.37s, were flown to Romania, where they were used subsequently by the Romanian air force. A developed version of the P.37 had been planned under the designation P.49 Mis (teddy bear), intended to be powered by engines of up to 1,600 hp (1193 kW). A prototype was under construction, but with the German advance on Warsaw it was destroyed to prevent it from falling into enemy hands.

Variants

PZL P.37A Los A - The first prototype, the P.Z.L. P.31/I, was flown initially in late June 1936 and successful testing of this aircraft, which was powered by two 873 hp (651 kW) Bristol Pegasus XII radial engines, led to a contract for 30 under the designation P.37A Los A.

PZL P.37C - A total of 35 P.37C bombers powered by 970 hp (723 kW) Gnome-Rhône 14N.07 engines intended for Bulgaria (15) and Yugoslavia (20), but never completed.
PZL P.37D - A total of 40 P.37D bombers with 1,050 hp (783 kW) Gnome-Rhône 14N.20/21 engines intended for Romania (30) and Turkey (10), but never completed.

PZL P.37B Los B - An improved version which introduced a revised cockpit canopy, twin-wheel main landing gear units and Pegasus XX engines. Deliveries began in late 1938 with only 70 aircraft being produced out of the 100 ordered.

PZL P.49 Mis (teddy bear) - A version of the P.37 had been planned under the designation P.49 Mis (teddy bear), intended to be powered by engines of up to 1,600 hp (1193 kW). A prototype was under construction at the time of the German invasion, but it was destroyed rather than have it fall into German hands. 

Specifications (PZL P.37B Los B)

Type: Four Seat Medium Bomber

Design: Panstwowe Zaklady Lotnicze Design Team led by Jerzy Drabrowski

Manufacturer: Panstwowe Zaklady Lotnicze in Poland

Powerplant: Two 925 hp (690 kW) P.Z.L. built Bristol Pegasus SS radial engines.

Performance: Maximum speed 277 mph (445 km/h) at 11,155 ft (3400 m); service ceiling 30,000 ft (9145 m) without bombload.

Range: 932 miles (1500 km) on internal fuel with 4,850 lbs (2200 kg) bombload.

Weight: Empty 9,436 lbs (4280 kg) with a maximum take-off weight of 19,621 lbs (8900 kg).

Dimensions: Span 58 ft 10 3/4 in (17.95 m); length 42 ft 4 3/4 in (12.92 m); height 16 ft 8 1/4 in (5.09 m); wing area 575.89 sq ft (53.50 sq m).

Armament: Three 7.7 mm (0.303 in) KM Wz. 37 machine guns in nose, dorsal and ventral positions, plus a bombload of up to 5,688 lbs (2580 kg) carried internally.

Variants: P.37A Los A, P.37C (Bulgaria & Yugoslavia but never completed), P.37D (Romania & Turkey but never completed), P.37B Los B, P.49 Mis.

Avionics: None.

History: First flight (prototype) June 1936; production completed (P.37A Los A) 1938.