The A-36A-1-NA "Apache" (although Apache was the A-36A's official name, it was rarely used) joined the 27th Fighter Bomber Group composed of four squadrons based at Rasel Ma in French Morocco in April 1943 during the campaign in North Africa. The 27th had a mixed component of Douglas A-20 Havocs and A-36As while the second operational unit, the 86th Fighter Bomber Group (Dive) arrived in March 1943 with the first pilots trained and qualified on the A-36A. On 6 June 1943, both of these A-36A units flew combat missions directed against the island of Pantelleria. The island fell to Allied attack and became the home base for the two A-36A groups during the invasion of Sicily. The A-36A proved to be a potent weapon; it could be put into a vertical dive at 12,000 ft (3,658 m)with deployed dive brakes, thus, limiting the dive speed to 390 mph (628 km/h)("A36A-1 Flight Manual requires deployment before starting a dive"). Pilots soon recognized that extending the dive brakes after "peel-off" led to some unequal extension of the brakes due to varying hydraulic pressure, setting up an invariable slight roll which impeded aiming. Proper technique soon cured this anomaly and, subsequently, pilots achieved extremely consistent results. Depending on the target and defenses, the bomb release took place between 2,000 ft and 4,000 ft (610 and 1,219 m), followed by an immediate sharp "pull up."
Dive brakes in the wings gave the A-36A greater stability in a dive; however, a myth has arisen that they were useless due to malfunctions or because of the danger of deploying them and that they should be wired closed. Capt. Charles E. Dills, 27th Fighter-Bomber Group, 522d Fighter Squadron, XIIth Air Force emphatically stated in a postwar interview: "I flew the A-36 for 39 of my 94 missions, from 11/43 to 3/44. They were never wired shut in Italy in combat. This 'wired shut' story apparently came from the training group at Harding Field, Baton Rouge, LA."
However, tactical reconnaissance training with P-51 and A-36 aircraft had delivered some disquieting accident rates. At one time, A-36 training had resulted in the type having "the highest accident rate per hour's flying time" of any USAAF aircraft. The most serious incident involved an A-36A shedding both wings when its pilot tried to pull out from a 450 mph (724 km/h) dive. Combat units flying the A-36A were ordered to restrict their approach to a 70° "glide" attack and refrain from using dive brakes. This order was generally ignored by experienced pilots but some units did wire dive brakes shut until modifications were made to the hydraulic actuators. Nevertheless, the A-36 was used with great success as a dive-bomber, acquiring a reputation for precision, sturdiness and silence.
By late May 1943, 300 A-36As had been deployed to the Mediterranean Theater, with many of the first batch sent to the 27th to re-build the group following losses as well as completing the final transition to an all-A-36A unit. Both groups were actively involved in air support during the Sicilian campaign, becoming especially adept at "mopping" up enemy gun positions and other strong points as the Allies advanced. During this operation, the 27th Group circulated a petition to adopt the name "Invader" for their rugged little bomber, receiving unofficial recognition of the more fitting name. Despite the name change, most combat reports preferred the name "Mustang" for all of the variants. The Germans gave it a flattering, if fearsome, accolade, calling the A-36As: "screaming helldivers."
Besides dive bombing, the A-36A racked up aerial victories, totaling 84 enemy aircraft downed and creating an "ace", Lieutenant Michael T. Russo from the 27th Fighter Bomber Group (ultimately, the only ace using the Allison-engined Mustang). As fighting intensified in all theaters where the A-36A operated, the dive bomber began to suffer an alarming loss rate with 177 falling to enemy action. The main reason for the attrition was the hazardous missions that placed the A-36A "on the deck" facing murderous ground fire. German defenses in southern Italy included placing cables across hill tops to snare the attacking A-36As. Despite establishing a "reputation for reliability and performance, "the one "Achilles' heel" of the A-36A (and the entire Mustang series) remained its vulnerable cooling system leading to many of the losses By June 1944, A-36As in Europe were replaced by Curtiss P-40s and Republic P-47 Thunderbolts.
A-36As had also served with the 311th Fighter Bomber Group in the China-Burma-India theater. The 311th had arrived in Dinjan, India by late summer 1943 after being shipped across the Pacific via Australia. Two squadrons were equipped with the A-36A while the third flew P-51As. Tasked with reconnaissance, dive bombing, attack and fighter missions, the A-36A was outclassed by its main opposition, the Nakajima Ki-43 "Oscar." The light and highly agile Japanese fighter could outmaneuver the A-36A at all altitudes but did have some weak points: it was lightly armed and offered little protection for pilot or fuel tanks. However, the A-36A fought at a significant disadvantage, having to carry out long-range missions often at altitudes above the "Hump" that meant its Allison engine was below peak performance. In a fighter escort mission over Burma, three A-36As were lost without scoring a single victory. The A-36A CBI missions continued throughout 1943–1944 with indifferent results. The A-36A remained in service in small numbers throughout the remaining year of the war, some being retained in the US as training aircraft.
"The type's relatively brief service life should not camouflage the fact that it made a major contribution to the Allied war effort" especially in the Mediterranean and it amounted to the first USAAF combat use of a Mustang variant. The effectiveness of the A-36 as a ground attack aircraft was demonstrated on 5 June 1944. In a well planned attack on the large, well defended rail depot and ammo dump at Orte, Italy, Lieutenant Ross C. Watson led a flight of four A-36s through a heavy overcast on the approach to the target. Watson's A-36s scored several hits under intense anti-aircraft fire while Lt. Watson's aircraft was hit and damaged by ground fire. Under continuing heavy ground fire. Lt. Watson pressed home his attack and destroyed the ammo dump before making an emergency landing at an advanced Allied airfield.