The biplane with the largest production run in aviation history was the Po-2. An astonishing 40,000 plus were produced between 1928 – 1953. The Po-2 was a general purpose biplane that was used in military and civilian roles as a trainer, crop-duster, ground attack, and observation platform.
Originally named the U-2, it was designed by the Soviets to replace the U-1, which was the Avro 504 as used for training. One of its uses was as a psychological warfare weapon as it attacked out of nowhere in the night to deprive German troops of sleep.
This type was also used by the “Night Witches” of the all-female 588th Night Bomber Regiment who flew as many as 18 low altitude night raids in a single night, harassing German rear-area positions. The Po-2 was almost impossible to shoot down due to tactics, low stall speed, and a tight turn radius.

Country: Russia
Manufacturer: Polikarpov
Engine: Shvetsov M11D Radial
Horsepower: 125 hp
Max Speed: 94 mph
Weight: 2976 lbs
Ceiling: 8,843 feet
Crew: Two
Armament: 1 x 7.62mm ShKAS MG

The Stinson L-5 Sentinel was developed for the Army from the civilian Stinson Voyager. The L-5 served in observation and support roles as a light and nimble aircraft that would operate out of almost any small field available.
L-5’s were capable of taking off in as little as 50 feet with full flaps, earning the name of the “Flying Jeep”. The plane could deliver messages and supplies to front line areas and evacuate casualties in a “litter” behind the pilot when the observers' seat was not needed.
During the Korean war, Marine L-5’s (USMC designation OY) even operated from a carrier.

Country: USA
Manufacturer: Stinson
Engine: Lycoming 6 cylinder
Horsepower: 190 hp
Max Speed: 128 mph
Weight: 2200 lbs
Ceiling: 15,800 feet
Range: 390 miles
Wing Span: 34′ 10″
Crew: Two