How did friendly fire play a part in WWI and WWII?

Perhaps the most famous incident of friendly fire in WWII occurred in Operation Cobra. This was the planned breakout from Normandy, and it featured a massed preparatory bombardment by heavy bombers. While the Army wanted the planes to bomb parallel to the front lines to minimize the risk of friendly fire from “bomb creep” (where successive waves of bombs hit beyond the target) there were technical restrictions that cause the bombers to adopt a perpendicular approach. The bombardment devastated German lines, with many of the defenders killed or incapacitated by the assault. The Panzer Lehr Division was “crippled.” (Inferno, Max Hastings, pg 536) The feared bomb creep did occur, and friendlies were hit as well. Over a hundred American troops were killed, and nearly five hundred were wounded. This included the highest ranking US soldier killed in the European Theater of Operations—Lieutenant General Lesley McNair. Cobra suffered a short delay before being highly successful.

While the use of heavy bombers did facilitate Cobra’s breakout, there was a reticence to use such bombers in future operations. First, there were fears that a repetition of friendly fire would happen again. Also, there was a feeling amongst bomber commanders that taking the bombers away from their strategic missions was a mistake at worst, or a detour at best. Lastly, medium bombers and fighter-bombers could apply much of the same effect without as much risk while the heavy bombers could do effective interdiction of transportation further behind the lines. Later, increases in accuracy allowed heavy bombers to return to a tactical role, especially in Vietnam during the siege of Khe Sanh.