Tupolev SB in Soviet Service. Part Three.

 

The Tupolev SB was Soviet's main bomber during the Winter War. During this conflict, ranging from late November 1939 until until mid March 1940, the VVS deployed more than 3.000 aircraft to defeat the Finns who had only 145 aircraft in their ranks.
As we said, the Tupolev SB was VVS' main bomber and it flew the first Soviet attack against Finnish soil, which was an attack against Helsinki, the Finnish capital city. As the winter was really harsh, many Tupolev SB 2M-100As were equipped with skis and some few of them were equipped with the, back then, experimental MV-3 rear turret. The RS-132 unguided rocket was also tested in this conflict as six Tupolev SB 2M-100As were fitted with rocket launching equipment on the wings. These rockets were mainly used against ground targets.
As the war progressed on, with a furious Finnish resistance, many Tupolev SB of various types were captured by the Finnish who repaired them and push them into service with the Ilmavoimat (Finnish Air Force). 
The war ended on 13th March 1940 with the Finnish agreeing to yield a buffer zone to the Soviets. However, casualties on the VVS side were enormous, estimated at a number between 700 and 900 aircraft, half of them bombers. 

The Tupolev USB was the trainer variant of the regular SB which came out almost two years after the first SB rolled out of the factory in 1936. It was based on a SB 2M-100A and was built at GAZ (State Aircraft Factory) 22 at Fili, Moscow. The whole nose section was remodelled to install a second open cockpit for the instructor. The step was relocated from the front to the rear of the starboard nose. A windshield was installed for the instructor's compartment but no canopy was provided. Instructor's cockpit had similar controls to those in the pupil's cockpit, however, they were automatically disconnected when the instructor took command. In spite of the importance of communication between the instructor and the pupil, the USB lacked an intercom. The instructor accessed his cockpit using a ladder placed through the open ventral hatch doors.
The USB prototype underwent State Acceptance Trials between 11 and 16 March 1938. During those tests it was equipped with non-retractable ski undercarriage. GAZ 22 at Fili completed just a few USB, as most of them were converted in the field from existing Tupolev SB of every kind. 

Sources:

1st Signal Squadron - Aircraft In action 194 - Tupolev SB in Action

2nd https://en.wikipedia.org/wiki/Tupolev_SB
3rd https://en.wikipedia.org/wiki/Winter_War