Performance specifications of the P.37 included a maximum speed of 256 miles per hour, a range out to 1,615 miles and a service ceiling up to 23,000 feet. Rate-of-climb was 925 feet-per-minute.
Variants were led by the P.37/I prototype and this differed in having a single-finned tail unit. The P.37/II was another prototype incorporating various improvements as well as introducing the twin-finned tail arrangement. The first ten aircraft of the series were designated P.37bis and carried the single-finned tail unit of the first prototype as well as 2 x Bristol Pegasus XIIB series engines. The P.37Abis followed through a batch of nineteen aircraft and had twin-finned tails.
The definitive production model became P.37B (I/II) and carried twin-finned tails as well as in-house PZL Pegaz XX series air-cooled radial piston engines of 970 horsepower output (each).
P.37C and P.37D were proposed versions with Gnome-Rhone 14N-01 and 14N-21 engines respectively - neither were produced. The P.49 Mis was another proposed bomber variant based on the P.37 but only a single incomplete prototype was made as the German invasion halted its development.
During the war, the bomber operated with the 10th and 15th Bomber Squadrons of the Polish Air Force. Deliveries began in early-1938 but a limited supply of engines meant that operating strength was slow to achieve. At the time of the German invasion of Poland in September of 1939, about 86 were on hand to defend though, in the subsequent fighting, fewer than 50% of the stock were actually pressed into service. When used in bombing sorties, the bombers were sent airborne with less than the intended bomb load due to operating from unprepared airfields which limited their tactical and strategic value. As the invasion pressed on, losses of the series mounted as no fighter escorts were provided - making these large targets juicy pickings for German pilots. Before the end, about 25 of the stock were flown to Romanian where they were interred by local authorities (and reconstituted for service in the Romanian Air Force and used until mid-1944). Some 30 P.37 bombers were destroyed by the Poles before they could be captured by the Germans.
Planned pre-war customers for the P.37 included Belgium, Bulgaria, Greece, Spain, Turkey and Yugoslavia.
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