The F2A-1s diverted to Finland were given the company designation B-239. The naval equipment (tail hook, life raft, catapult harness) was removed, and the telescopic sight was replaced by a simple bead and sight arrangement. Armament consisted of one 0.30-in and one 0.50-in machine gun in the cowling, plus two 0.50-in machine guns in the wings. The engine was replaced by an export-approved 950 hp Wright R-1820-G5 radial. Maximum speed was 297 mph at 15,580 feet and service ceiling was 32,500 feet. Empty weight was 3900 pounds, and maximum weight was 5820 pounds.
The B-239s were transferred to Finland via Trollhattan, Sweden, where they were assembled by Norwegian Air Force mechanics. They were then ferried to Finland by both American and Finnish pilots. Only six examples had reached Finland by the time that the Russo-Finnish "Winter War" ended on March 3, 1940. During the uneasy peace that followed, Finnish personnel made a number of modifications to their Brewsters, including the installation of an armored headrest and seat back, plus a reflector gunsight in place of the original bead and ring.
A total of 44 B-239s reached Finland, and they were assigned the Finnish serial numbers BW-351 through BW-394. The B-239s were assigned to Lentolaivue 24 (LeLv 24), 32 being used on active duty and the rest held in reserve.
Finland went to war against Russia again on June 25, 1941, this time allied with Germany. During the first few months, the Brewsters were able to maintain air superiority over the northern front. The Finns found the Brewster to be very maneuverable at low level. B-239s encountered LaGG-3s, Yak-1s and Yak-7s, as well as Lend-Lease Hurricanes, P-40s and P-39s. The highest-scoring B-239 ace was Hans Wind, who got 39 of his 75 kills flying the B-239. The leading Finnish ace, Eino Juutilainen, scored 34 of his 94 kills while attached to LeLv 24 flying Brewsters.
As the war with Russia wore on, maintenance of the Finnish B-239s became an increasingly serious problem, since Finland was now allied with Germany and no longer had access to American spare parts. In an attempt to overcome these problems, at least six B-239s were fitted with captured Russian M-63 radials (these were license-built versions of the Wright Cyclone). The Finnish State Aircraft Factory also began the development of a homebuilt version of the B-239, this with a captured M-63 engine and plywood wings. This aircraft was known locally as the Humu. However, only one prototype was built. After the war, the Humu prototype was restored and is on display in a museum in Finland.
Experiments were made with ski landing gear for operations from snow-covered fields. However, the landing gear could not be retracted when the skis were fitted, and this severely degraded performance. Consequently, skis were rarely used operationally.
In 1944, LeLv 24 traded in its surviving B-239s for Messerschmitt Bf 109G-2s. These B-239s were transferred to HLeLv 26. Kills continued to be scored, but by this time the Soviets had deployed large numbers of high-performance fighters and losses of B-239s began to mount. HLeLv 26 continued to operate its B-239s until the end, when an armistice was signed with the Soviets on September 4, 1944. Finland then switched sides and began to drive German forces out of Finnish territory. The Brewsters were flown against retreating German forces in Lapland, scoring several kills against Ju-87 Stukas.
After five years of combat and attrition, only eight Brewsters remained in the Finnish inventory. These surviving Finnish Brewsters were used in the training role until late 1948. During its combat career, the B-239 is credited with 496 kills, against 19 losses, for a victory ratio of 26 to 1. Finnish air force records credit 41 kills to a single B-239 before it was shot down. The overall kill rate was 26 to 1, and Brewster pilots shot down a total of 477 Soviet aircraft for a loss of only 19. Is there any other fighter aircraft in history which has a record as good as this?
Serial number BW-372 went down in a lake in Russian Karelia during a dogfight in 1942, and was lifted from the lake in 1998. After some dispute over the ownership of the plane, it was decided that it was still US Navy property, and the plane ended up in National Museum of Naval Aviation in Pensacola, Florida. However, it has been returned to Finland for restoration, but will be returned to Pensacola after the restoration is complete. It is believed to be the sole surviving Buffalo in the world today.