PZL.46 Sum (sheatfish) was a light bomber developed by Państwowe Zakłady Lotnicze shortly before World War II, which, was directed to serial production in the spring of 1939.

It was a rare feature in light bombers' construction and its usefulness was questionable, as it reduced performance).

Bulgaria, using PZL.43 bombers, showed an interest in the new design and made a preliminary order for 12 aircraft, uncompleted due to war.

Stanisław Prauss made also a preliminary design of smaller development variant PZL Łosoś, which was to be a two-seater dive bomber with 1,600 hp (1,200 kW) Hispano-Suiza 12Z inline engine and retractable landing gear, without underbelly gondola.

The bombardier's combat station was in a gondola underneath the fuselage, where he also operated an underbelly machine gun.

On 26 September 1939, under pretext of delivering the plane to IAR factory in Brasov, it was flown by Riess with other three crewmen (including Witold Urbanowicz) from Romania to besieged Warsaw.

On 27 September 1939, with most of the Polish territory occupied by Germans and Soviets, it flew to Kaunas in Lithuania.