Three A-20G blocks were represented via 50 total A-20G-5's, 300 total A-20G-10's and 150 total A-29G-15's. These held 4 x 12.7mm machine guns in the solid nose with additional 2 x 12.7mm machine guns to the lower forward portion of the fuselage (ala the A-20A, A-20B and A-20C models). The dorsal 12.7mm and ventral 7.62mm armament remained the same as in the A-20G Block 5 models. Block 10 and Block 15 incorporated other more subtle changes including increased armor protection based on operational feedback. Beginning with Block 20 (through Block 45), the dorsal 12.7mm armament on a flexible mount was upgraded to a powered-turret fitting. Four outboard under wing pylons were also added on a new reinforced wing.
The A-20H was a limited-production run model numbering 412 aircraft for use by American and Soviet forces (via Lend-Lease). These represented similar models to the A-20G (Block 45) but with more powerful engines allowing for shorter take-offs. Essentially, A-20H models were "improved" A-20G models with Wright R-2600-29 Cyclone supercharged radial engines of 1,700 horsepower each. By this time the R-2600-3 series was out of production.
A-20J models were "lead ship" variants with glassed-in nose assemblies as requested by the USAAC. These aircraft were pivotal in increasing the bombing accuracy of the solid nose A-20G models as they featured dedicated bombardiers complete with Norden bombsights and would often "lead" the other "sightless" bombers to the target, achieve the appropriate drop time via direct sighting and inevitably drop its bombload, signaling the other A-20's in the flight group to do the same. A-20J's were essentially the same aircraft with the exception of their nose construction. As might be expected, the 4 x 12.7mm machine guns were removed in the A-20J models to make room for the bombardier and his equipment. The 2 x 12.7mm lower-fuselage machine guns were, however, still kept as standard armament in the type those there were sometimes deleted in the field for the simple idea of saving weight. Total production of the A-20J was 450, built concurrently alongside the A-20G for ease. The A-20J was eventually replaced by the A-26C Invader aircraft, this airplane with its own glassed-in nose. A-20K models were similar in design and scope to A-20J models, serving as lead ships though based on the A-20H and mounting different engines (Wright R-2600-29 Cyclone radials of 1,700 horsepower).
The P-70 became the dedicated (albeit interim systems until the arrival of the Northrop P-61 Black Widows) night-fighter variants of the A-20 series. The P-70A featured AI radar in a solid nose along with 2 x Wright R-2600-11 radial engines of 1,600 horsepower. 39 P-70A-1's were delivered in 1943 to help combat Japanese night raids in the Pacific. Armament of these P-70A-1's included an under-fuselage pack containing 4 x 20mm cannons and two machine guns in the dorsal position. The former was later changed to 6 x 12.7mm machine guns in the nose. The P-70A-2 appeared as 65 converted forms from A-20G models but were basically similar to the P-20A-1's without the rear defensive machine guns. The P-70B-2 followed and was a night-fighter trainer platform appearing as 105 converted A-20G and A-20J models with American-made SCR-720/-729 series radar systems.
The CA-20 was another notable variant, these being A-20's converted for general transportation roles as the newer A-26 Invader took more and more of the A-20's role away from it. These aircraft astoundingly served into the 1960's.
Like the British before them, the Americans subjected the A-20 airframe to a series of experiments. Jet Assisted Take Off (JATO) was a popular experimental approach to most any airframe during the war and the A-20 was no exception. GALCIT JATO units were installed in the aft portion of each engine nacelle and tested in April of 1942. A reconnaissance attempt produced an A-20 with a K-24 camera system mounted in the tail. One A-20 had her nose armament removed in favor of a trial 4 x gun blister package attached to the fuselage sides. Another more interesting experiment saw an A-20 with her main landing gears converted to tractor-style tracks for operations in mud, snow and generally any surface unusable by traditional aircraft. Needless to say, these aircraft served as nothing more than experiments with most going the way of the dodo, though some still serving a viable research-minded purpose nonetheless.
The basic A-20 design featured a deep cylindrical fuselage with middle mounted cantilever monoplane wings, each containing a radial three-propeller engine slung under the wing in an extended engine nacelle. The empennage was traditional, sporting a single vertical stabilizer and cantilever horizontal planes. The undercarriage was of a tricycle arrangement with two main wheels recessing into each engine nacelle and a nose gear with a single wheel recessing rearwards just under the cockpit floor. The engine nacelles on either wing assembly came to a point well past the wing trailing edge, giving the A-20 its distinct top-down silhouette. A rear gunnery/observation position was set at the top of the base of the empennage while a ventral gun "tunnel" position could also be utilized. The cockpit provided good views all around and helped offer up the feel of the A-20 as a fighter more than a bomber. In all, the aircraft proved structurally sound and suited to the work bestowed upon it, proving a success for the Douglas company as well. Like many of the larger aircraft in the Second World War, the airframe of the Havoc was duly noted for its ability to withstand a great deal of damage while keeping her crews alive. Additionally, the airframe proved quite adaptable by a variety of users utilizing a variety of armament and internal systems. Power for the type was provided by a long line of Wright radial series engines of various power specifications.
Armament varied throughout the course of the aircraft's production life, particularly when basing it on the operator. Standard fare included a battery of 4 x 12.7mm machine guns housed in a solid nose supplying the aircrafts offensive forward "punch" along with a dorsal position mounting a flexible machine gun (or a pair of such weapons). Additionally, this punch could be enhanced through the use of internally held bombs - a bombload of up to 4,000lbs - which a portion of this load could be used for additional fuel. It was not uncommon for the nose-mounted armament to be increased in the form of 6 x 12.7mm machine guns for a truly imposing forward-strike potential. Other armament included a pair of defensive 12.7mm machine guns held in the rear cockpit and a single 12.7mm machine gun in a ventral position reached via a tunnel. Blister gun packs were not uncommon as were lower-fuselage 12.7mm machine guns. 4 x 20mm cannons were attempted in the solid nose assembly as was a 1 x 37mm cannon arrangement.
As with any aircraft, the cockpit of the A-20 series was the heart of the plane. One must keep in mind that the A-20 was really designed as a light bomber, though it was piloted by just one personnel in the single-seat cockpit and was, for all intents and purposes, designed as a heavy fighter. The cockpit was positioned forward in the design with a glazed canopy, offering up stellar views forward, above and to the sides (including rear sides). The framed canopy door swung open on a hinge mounted along the starboard side of the frame and allowed for easy entry and exit from the seat. Maneuvering the aircraft was accomplished through a traditional control wheel mounted on a flexible column. The gun button was fitted to the top right portion of the control wheel for easy access. Throttle, mixture and propeller controls were fitted in a cluster to the left side of the seat as were the various electrical switches. The main board was noted for its well-placed dials and gauges. Fuel tank controls, bomb selector, radio and cockpit heating functions were placed to the right of the pilot's seat. In all, the cockpit was approved of by both American and British airmen alike. If there was any complaint from pilots, it was in the use of framing for the cockpit window, restricting viewing to some extent, particularly in poor weather.
A-20's served in Pacific and European Theaters of War. The 3rd, 312th and 417th Bomb Groups represented Havoc use in the Pacific whilst the 47th, 409th, 410th and 416th Bomb Groups utilized the type in an early limited role in Europe. Operations in the latter were held by the 9th Air Force with the 9th Bomber Command. On July 4th, 1942, twelve A-20 Havocs (6 with American airmen and 6 with British airmen) launched a low-altitude daylight bombing raid on four Dutch airfields marking the first such US raid in the European Theater. These American-flown Havocs were part of the 15th Bombardment Squadron.
A-20's converted as interim night-fighters became the P-70. P-70 Havocs were sent in bulk to the 18th Fighter Group and saw action in support of ground forces over Guadalcanal, Bougainville and the Solomons. P-70's were eventually replaced by the newer and more capable Northrop P-61 Black Widows beginning service in 1944. Black Widows offered up improved overall performance, impressive cannon/machine gun firepower and high-altitude performance and was a dedicated platform specifically designed for night operations.
Soviet forces were the other real major operator of the aircraft, making headway with the platform as a ground attack fighter by bringing its impressive nose-mounted armament to bear on unsuspecting ground foes. Additional actions saw the A-20 operating in the Middle East and North Africa.
Production of any A-20 system was ended in September of 1944 after which some 7,385 to 7,478 were produced.
The A-20 proved a little aircraft of large worth. The ability for the system to adapt to various armament configurations allowed for the type to reach further and deeper into the war than it would have otherwise. The Havoc proved to provide its operators with a sturdy and powerful attack platform capable of under taking a variety of specialized roles from ground attack to light bombing and strafing as needed. In any form, A-20 Havocs proved that "tweener" type, twin-engine designs still had a place in a war dotted with sleek fighters and heavy bombers.