When the American troops landed in North Africa beginning of 1943 as part of Operation Torch, they suddenly had to face a battle hardened German / Italian army, lead by the legendary Erwin Rommel. The results showed quickly in Tunisia, where they suffered a significant defeat at the Battle of Faid Pass, falling for a typical German trick. After attacking US positions, the Axis forces quickly retreated, encouraging the battle hungry 1st Armored Division to take pursuit. They were however lead right in front of a screen of 88mm anti-tank guns, that slaughtered nearly all of the pursuing US armored forces in a matter of minutes.
With this defeat, the Allied forces had to fall back to Kasserine Pass, a 3km wide gap in the Atlas Mountains, leaving most of Tunisia to the Axis. Rommel having seen the inexperience of the American forces urged the offensive to continue, and while his orders did not fully reflect his proposed strategy, the offensive continued 2 days later. Rommel commanded the 10th Panzer Division personally, attacking Kasserine Pass head on with a large portion of his forces.
The tactic worked and the American troops were in constant retreat, at times so disorganized that the Germans could capture heavy equipment left behind. They especially held the M3 armored half-tracks in high esteem. The fact that so many American positions have been overrun actually slowed down the offensive, as more and more troops had to stay behind to eliminate the pockets of resistance. Still, by the end of the day the US forces were pushed back as far as 80km-s behind their original lines at the start of the offensive.
Allied reinforcements were close however, and the next day more experienced British troops reinforced the front lines, while a hastily formed but powerful American-British-French artillery force started to rain death on the attackers. Under such heavy bombardment, and in fear of getting out-flanked by British forces through Libya, Rommel decided to call off the offensive and the Allied forces could re-occupy their positions in the next days. While the Axis offensive failed, the losses were significant on the Allied side with a casualty of 10.000 with close to 200 tanks destroyed, compared to the 2000 loss of the Axis with a mere 34 tanks taken out.
This shocking start was a huge wake up call to the US Army, and sweeping changes were made to improve the situation. The command of the II. Corps was handed over to a certain Major Patton, the coordination of artillery and air-support was improved drastically, anti-aircraft strategy has been reformed having learned that the Axis air-raids almost exclusively focused on the Allied artillery batteries, and last but not least, pure light tank battalions have been disbanded and used later in a reconnaissance role only. By the time the invasion of Sicily started, the American forces were considerably stronger due to a direct result of these changes.