The radio operator was also charged with defense of the sides of the aircraft so at his station were 0.50 caliber Browning M2 heavy machine guns - one set to either fuselage side and each gun given 600 rounds of ammunition. Originally, the machine guns were installed through structural "blisters" found along the sides of the fuselage.
Optional armament for the bomber destroyer role was 20 x 30lb fragmentation drop bombs carried within a bomb bay. The destroyer was expected to cross over a slower-moving enemy formation and attempt to score a rather tricky direct hit on the group of moving targets by dropping a lethal load.
First flight of what was designated the XFM-1 was on September 1st, 1937. Due to the growing weight of their new aircraft, engineers substituted the original Allison V-1710-9 for an Allison V-1710-13 of 1,150 horsepower output. The optimistic and complex aircraft was to provide a myriad of challenges for Bell personnel for most of its active testing life - it was not a favorite amongst test pilots charged with flying the machine nor ground crew charged with its upkeep and repair.
During firing tests, the nacelle-mounted tracer machine guns were found to be wholly inadequate for the aiming required of the M4 cannons with their larger, heavier 37mm projectiles. As such, a specialized device provided by Sperry Instruments was installed which added a telescopic rangefinder and gyro-stabilized autopilot feature in which the pilot could fire the cannons instead. The nacelle crewmen were retained for they were still required to reload the five-round clips into the weapons when needed.
Despite these early failings, the USAAC allowed the XFM-1 product to continue when it awarded another contract during May of 1938 for thirteen test aircraft under the designation of "YFM-1". Testing of the series then continued into 1939 and, at this point, the aircraft had been modified with an enlarged vertical tail fin. The propeller units each received smaller spinners and the waist machine gun blisters were omitted and revised through a more streamlined approach. The more advanced YFM-1 was now outfitted with Allison V-1710-23 series engine of 1,150 horsepower each and had its turbosuperchargers relocated. Structurally, the aircraft's skin was made more streamlined thanks to the use of flushed rivets which helped to limit overall drag along the surface of each panel in play. A retractable dorsal turret was armed with a sole 0.30 caliber machine guns while another 0.30 caliber machine gun was manned through a ventral "tunnel" to help defend the critical lower rear quadrant of the aircraft. The bomb load was updated to carry up to 600 lb of conventional USAAC drop bombs.
The YFM-1 did not achieve a first flight until September 28, 1939 - some two years after XFM-1 first flew. The second flight suffered damaged when one of the turbosuperchargers fell apart in-flight but the program was still evolved by the USAAC to the point that it was eventually passed on to its airmen for formal testing from February of 1940 onwards. The YFM-1 standard was realized through nine aircraft coming in 1940. Three more were delivered into October with rather forward-thinking tricycle undercarriages - a modern approach revisited by Bell in their upcoming P-39 fighter. These aircraft carried the slightly altered designation of "YFM-1A". Two other Airacuda aircraft of the batch appeared with Allison V-1710-41 engines of 1,090 horsepower output though they lacked their turbosuperchargers. These forms were designated "YFM-1B" and emerged from the existing YFM-1 stock.
Service trials began during 1941. One example had already been lost during a forced landing brought about by a locked rudder - no fatalities were recorded but the airframe was wrecked. Another airframe was lost in an accident occurring during January of 1942.
Despite all of the work and funding poured into the Airacuda program, interest in the large aircraft was being lost to American warplanners. The United States officially entered the war in December of 1941 following the Japanese attack on Pearl Harbor and more pressing matters required attention in the war effort. The Airacuda was tested as far as needed but its design was never wholly sound - engine cooling remained an issue through all of its life requiring prototypes to be towed to their take-off spots rather than running themselves into position. The pusher propellers represented quite a danger to exiting crewmembers should they ever be called to bail out of the aircraft - they would have to pass through the gauntlet of spinning blades and avoid the vertical tail unit to survive. Finally, despite whatever engine was fitted, the heavy aircraft could simply not match the performance expected of it in keeping up with the new B-17 bomber fleet - its maximum speed was no more than 277mph with a cruise speed of 244mph (B-17Gs eventually reached maximum speeds of 287mph). Couple all this with the fact that the technology-laden aircraft became an expensive product to procure and maintain and it ultimately proved a failed venture for Bell and a forgettable product to the USAAC.
The focus fell back to single-engine fighter mounts with their inherent agility. These eventually were also modified to carry bomb loads in the fighter-bomber role. Better twin engine options eventually became available to the USAAC, particularly when the Lockheed P-38 "Lightning" made its appearance. The P-38 went on to have a stellar wartime career and served in a myriad of roles over the battlefield. It was certainly a more compact offering when compared to the Airacuda and was piloted by just one crew while carrying bombs and rockets in addition to its standard cannon/machine gun armament mix.
None of the Airacuda airframes survived the war, being scrapped by early 1942.
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