On December 11, 1939, Belgium placed an order for 40 export versions of the F2A-2. These planes were given the company designation of Model B-339B. The Model B-339B was basically a de-navalized version of the F2A-2. The R-1820-40 engine was replaced by an export-approved 1100 hp Wright R-1820-G105 air-cooled radial driving a cuffed Curtiss Electric propeller. The naval equipment was removed, and the tail hook opening behind the tail wheel was faired over by a pointed tail cone, which made the fuselage slightly longer. The telescopic gunsight fitted to the F2A-2 was replaced by a fixed post gunsight. Four 0.50 cal machine guns were provided, two in the upper fuselage and two in the wings.
The US Navy had agreed to divert most of its F2A-1s to Finland in exchange for the promise that it would get an equivalent number of F2A-2s in their place. However, the Belgian government appealed to the State Department to allow their order to take precedence over the Navy order for F2A-2s, and the Navy reluctantly agreed to the delay. The production of the B-339B began in early 1940.
The first B-339B (flight tested before delivery under the US civil registration of NX-56B) was on its way to Belgium when the German blitzkrieg overran the Low Countries, and the ship carrying the plane was diverted to France. This plane was apparently later captured by the Germans and was test flown.
The next six B-339Bs were diverted to France. They were sent to Canada and loaded aboard the French aircraft carrier Bearn, along with a batch of Curtiss SBC Helldivers and Curtiss Hawk 75A-4s that had been purchased for the Armée de l'Air. The Bearn sailed on June 16, 1940 and was in mid-ocean when France fell. The carrier was diverted to Martinique (a French possession), and the six Brewsters along with the other aircraft aboard were unloaded. They sat for months parked out in a field while international arguments took place about their true ownership and their ultimate destination. There was some concern on the part of the United States government that the Vichy regime in France might become an active German ally and that these aircraft might present a threat to the nearby Panama Canal. Finally, the planes sitting on Martinique were destroyed on the ground by sabotage, probably by Allied agents to prevent them from falling into Axis hands.
The 33 remaining B-339Bs in the Belgian order were diverted to Britain, the first example arriving in July of 1940. They were assigned the Air Ministry serial numbers AS410-437, AX811-820 and BB450. These serial numbers included the "Martinique Six", which Britain had tried unsuccessfully to obtain. The British fitted 0.303-in machine guns in the wings and 0.50-in guns in the fuselage. The Brewsters were tested by the American Eagle Squadron, which found them totally unfit for combat in Europe, since they lacked a reflector gunsight or self-sealing tanks. It was decided, therefore, that the B-339Bs were suitable only for overseas duty.
Eighteen B-339Bs were assigned to the Fleet Air Arm for service in the Middle East. No. 855 Squadron conducted brief deck trials aboard the HMS Eagle during March of 1941. Since the B-339Bs lacked carrier arrester hooks, the Buffalos engaged the arresting cables with their landing gear, which was an entirely unsatisfactory arrangement and further trials were discontinued. Some B-339Bs were sent to Crete for service with No. 805 Squadron of the Fleet Air Arm, but I don't think that they were ever flown in combat. All flyable aircraft were evacuated to Egypt the day before the German invasion of Crete on May 20, 1941. However, at least one unserviceable B-339B was left behind on Crete and was captured by the Germans. Eventually, No. 805 Squadron traded in its Brewsters for Grumman Martlets, and the survivors were relegated to training duties.