Curtiss A-18 (Shrike II) Ground Attack Aircraft
Limited to thirteen total examples, the Curtiss A-18 managed a short service life for the Americans and was replaced by more potent, advanced forms before the end.
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In the mid-1930s, the United States Army Air Corps (USAAC) began evaluation of a new twin-engined, twin-seat ground attack aircraft through the Curtiss XA-14 program. The design offered a very modern appearance coupled with exceptional performance for its time, the latter quality allowing the aircraft to outpace even some of the fastest fighters of the period. One test article was completed and this led to the developmental Y1A-18 and, ultimately, the A-18 "Shrike" designation. However total production only ever reached 13 aircraft as the A-18 series was, itself, outpaced by newer designs - the A-18 never materialized into a long-term USAAC solution as it was quickly superseded by more advanced forms.
The ground attack aircraft had increasingly grown in tactical value for warplanners heading into World War 2 (1939-1945). These platforms offered about the same firepower as a medium-class bomber but could also be used in the direct-attack role as a heavy fighter. Such flexibility was highly sought after by air services of the time and the A-18 seemingly fit the bill for the USAAC as its revised its stock of aging aircraft. The service went on to evaluate a small collection of twin-engined, twin-seat types prior to the Grand War.
The A-18 held roots in the original Curtiss Model 76 which was outfitted with a pair of Wright XR-1510 "Whirlwind" radial piston engines of 600hp each and driving two-bladed propellers. A monoplane design form was selected with the engines held in streamlined nacelles along the wing leading edges. The wings and engines straddled the slim fuselage which was aerodynamically refined. The crew of two sat under a relatively long, framed canopy. The tail unit was of a traditional arrangement featuring a sole vertical fin and low-set horizontal planes. The undercarriage was of a typical tail-dragger configuration.
After testing with the Model 76, the aircraft was revised with Wright R-1670-5 "Cyclone" engines of 775 horsepower (each) and driving "constant speed" propellers to help increase performance. Testing resumed which produced evermore slightly evolved models which trialed engines and weapons (including fitting Wright R-1820-47 "Cyclone" radials of 850 horsepower each with three-bladed propellers; cannon calibers as large as 37mm were also tested). Before the end, the design had become the Model 76A ("Shrike II") which was the basis for the definitive A-18 service test form appearing in 1936.
A-18s were delivered to the 8th Attack Squadron, 3rd Attack Group (Barksdale Field, Louisiana) from July to October of 1937 and these teams quickly showcased the aircraft to be an effective gunnery and bombing platform (bombs were carried in compartments within each wing assembly). The A-18 was then used in training for 1940. Despite this showing, there lay several weakness in her design that revealed themselves with operational use. Her undercarriage was prone to collapsing when landing or taking off and her engines led to an underpowered aircraft which, in turn, limited its bomb load capabilities. To further hamper her future reach in service to the USAAC, the design was an expensive investment at about $105,000 USD per single unit. Curtiss attempted to rectify some of her issues including offering the product with Wright R-1830 radials but the damage was done.
Despite its potential at the outset, the operational life of the A-18 proved short as the 8th Attack Squadron moved on adopting the newer Douglas A-20 "Havoc" (detailed elsewhere on this site) from 1941 on. There was also little foreign interest in acquiring the aircraft which held design roots in the mid-1930s - this all but doomed any future the A-18 was expected to have. What few examples of the A-18 remained flew throughout 1942 but the line was completely retired in 1943. None saw combat action in World War 2 but two operated by way of the 108th Reconnaissance Squadron over the Panama Canal Zone where they saw their last days in the sky.
The A-18 proved instrumental to the USAAC observers as the value of larger, heavier twin-engined multi-crew systems had revealed itself. A-20s and Martin A-26 "Invaders" became some of the more classic forms of this aircraft type to see service in World War 2.