The minimal effect of high altitude bombing raids on the Ploieşti refineries prompted Fifteenth Air Force planners on 10 June 1944, to lay on a low level dive bombing attack by 48 P-38s of the 82nd Fighter Group and 45 of 1st FG. Mechanical turnbacks reduced the force by 21 aircraft, nine from the 1st Group. En route to the target much of the 1st FG was separated from the main force by a navigational error. Part of the 71st Fighter Squadron observed and attacked 6 Dornier 217 bombers but underestimated the numbers of Romanian IAR 80s escorting the bombers. Although six fighters and two bombers were credited as shot down, the 71st lost 9 Lightnings. When the 82nd FG arrived in the target area, along with the 27th Fighter Squadron and one flight of the 71st, they found the Ploieşti defense forces fully alert and a protective smoke screen concealing the targets. Flak shot down 7 P-38s during the attack, and 2 more were lost in strafing attacks on the return to Italy. After the attack, the 27th Fighter Squadron engaged 30–40 Me 109s, claiming 4 destroyed, 2 probables, and 4 damaged, but lost 4 P-38s in the engagement. In all, the 1st Fighter Group had 14 P-38s shot down, its heaviest single day loss of the war, while claiming 18 kills, including five by a 71st pilot, 1st Lt. Herbert Hatch. The 82nd FG lost an additional 8 Lightnings.