Polish Navy's Riverine Flotilla, popularly known as the Pinsk Flotilla, operated in the Pripyat basin in eastern Poland (today's western Belarus), 
and was meant to act against the Soviets. In September 1939 they had no chance to fight against the Germans, and the ships were scuttled
after the Soviet invasion on 17 September.*
In "what if" scenarios they can be used against the Germans on the Vistula (in early 1920, during Polish-Soviet war, the monitors belonged to Vistula Flotilla, operating on the Vistula, but then they were moved to the east). *
*
Strongest vessels were six small monitors:*
- four of Danzig-built B-class (ORP "Warszawa", "Horodyszcze", "Torun", "Pinsk"), armed in 1939 in 3 x 75 mm guns*
- and two of Polish-built Krakow class (ORP "Krakow", "Wilno"), armed in 3 x 100 mm howitzers *
*
There were also:*
- three Z-class armoured gunboats (ORP "Zawzieta", "Zuchwala", "Zaradna"), armed in 1 x 100 mm howitzer and short 37 mm gun*
- one heavy armed craft (CKU) ORP "Nieuchwytny", armed in 40 mm AA gun and short 37 mm gun.*
*
Only in 1939 there was created the Vistula Detachment of the Riverine Flotilla, fighting against the Germans in September 1939.
Its strongest craft was a heavy armed craft "Nieuchwytny", beside it there were armed craft: KU-4, KU-5, Ku-6 and KU-30. *
*
Polish riverine flotilla also had several sidewheel armed steamers and a number of small craft, described separately. *

*
_____________[description by PIBWL]*