Yes, Rodan, finally!!!!!!
Nevertheless, it is more correct to name that heavy bomber as DB-2A because DB-A was a prototype of that model.
Short history:
the designer of DB-A was professor V.F. Bolkhovitinov from Zhukovsky Academy of Air Forces. And DB-A means "Dalny Bombardirovshchik-Academia" = "Long-range Bomber-Academy". That was the intermediate model between heavy bomber TB-3 and heavy bomber TB-7 (Pe-8).
The first prototype was built in November 1934 and its first flight took place in May 1935. DB-A was tested till the June 1936 and it was much better in specifications than the main heavy bomber of USSR of that period TB-3 (because of excellent aerodynamics with semi-retractable gear (2m wheels), closed cabins and turrets, operated hydraulically). There were special passes inside the wings, so mechanic could operate engines during the flight. It was found that DB-A could continue flight on two engines, but it was recommended to replace AM-34RN engines on AM-34RNV engines. Bomber had excellent manoeuvrability, but visibility from pilots' cabin was bad during take-off and landings.
In November 1936 DB-A broke two world records - the bomber reached 7032 m altitude with 10 t of cargos and 4553 m with 13 t of cargos. In May 1937 two new world records were broken - speed 280 km/h with 5 t of cargos at 1000 km distance and speed 246 km/h with 5 t of cargos at 2000 km distance.
That prototype after reequipment was named N-209 and given to the Department of polar aviation of the Main North Sea Route (Glavsevmorput). 12 August 1937 unarmed N-209 with additional fuel tank in bomb bay began the transarctic non-stop flight through the North Pole from USSR to USA (1st pilot - famous polar pilot and Hero of USSR S.A. Levanevsky). The last radio message from N-209 (13 August) said that the plane crossed the North Pole successfully, but one engine stopped and the plane began to ice.... And that was all, no further news. The plane disappeared in Arctic and 9-months USSR/USA rescue expedition with many ice-breakers found nothing. The plane was not found till now (it could crash and sank in Arctic Ocean, may be even near Alaska already. The second possibility - Levanevsky made an emergency landing somewhere in Arctic, crew members tried to repair the oil system unsuccesfully and died in Arctic in several weeks, plane sank later because of crack of ice. Or the crew repaired all systems, tried to take-off and crashed). That fatal accident could be the disadvantages of oil system (each engine had independent oil system) and heavy controllability during strong wind/icing. Bolkhovitinov was against that flight as the plane was unfinished, only prototype, also the preparations to that record flight were made in a hurry, only during 2 months. AFAIK new Arctic expeditions are planning to find the lost N-209
The second prototype
DB-2A was equipped with new powerful engines AM-34FRN with turbo compressors and variable-pitch propellers, also fully retractable gear was added instead semi-retractable. Armament was also strengthened: the bomber was equipped with new central electrical turret and two additional 7.62mm MG ShKAS in engine nacelles (crew increased also - 11 men). DB-2A had completely new cabins with improved visibility. New bomber was produced in small amount in 1938-1939 (12 were built from 16 ordered, air factory N 22 - 3 copies, air factory N 124 - the rest). The photo shows DB-2A as serial heavy long-range bomber.
But DB-2A became obsolete already, so it was replaced in production by much more modern TB-7 (Pe-8) in 1940. Nevertheless, it was planned to produce additional improved series of DB-2A during WWII (that idea was rejected).
In 1936 the experimental BDD was build (improved DB-A with 1240 hp engines M-34FRN and airtight cabins) and in 1939 the new modification of DB-2A was developed ("heavy cruiser" TK-1 with 3x20mm + 5x7.62mm + 8 RS missiles).
Specifications of DB-A: full weight up to 32 t; dimensions 24.4x39.5m; 4xAM-34RN engines, 970 hp each; speed 330-370 km/h; climbing rate 2.45 m/s; altitude 7730 m; range 4600 km; armament 4-6x7.62mm + 1x12.7(or 1x20)mm + up to 6 t bombs (3 t in bomb bay); crew 7 men. Bomber was equipped with two radio stations, autopilot and radio-compass.
Photos:
http://www.airwar.ru/image/idop/bww1/dba/dba-1.jpg (DB-A, disappeared in Arctic N-209)
http://www.airwar.ru/image/idop/bww1/dba/dba-4.jpg (DB-A, N-209)
http://www.airwar.ru/image/idop/bww1/dba/dba-3.jpg (DB-A on skis)
http://eroplan.boom.ru/planes/db-a/db-a_8.jpg (picture of DB-A)
http://www.airwar.ru/image/idop/bww1/dba/dba-5.jpg (DB-2A as serial heavy long-range bomber)
http://astronaut.ru/bookcase/books/chert1/foto/1-3.jpg (designer V.F. Bolkhovitinov to the left, 1st pilot S.A. Levanevsky to the right - before notorious flight to USA near N-209)
http://epizodsspace.testpilot.ru/bibl/c ... ga-2/3.jpg (the same day, just before the flight - V.F. Bolkhovitinov and crew members of N-209)
http://eroplan.boom.ru/bibl/baidukov/pi ... ct3-11.jpg (N-209 and its crew, left to right: radio operator N. Galkovsky, 2nd pilot N. Kastanaev, commander S. Levanevsky, air-mechanics G. Pobezhimov, N. Godovikov, navigator V. Levchenko)
http://www.saint-exupery.ru/content/rus ... Karta2.jpg (route of DB-A from USSR to USA through the North Pole, dotted line - where the plane disappeared)