Patton

General George S. Patton (George C. Scott) addresses an unseen audience of American troops, (based on his speech to the Third Army). The film version of the speech is heavily condensed, with much of the original vulgarity removed.
Following the humiliating American defeat at the Battle of the Kasserine Pass in 1943, Patton is placed in charge of the American II Corps in North Africa. Upon his arrival, he enforces discipline amongst his troops, e.g. fining a cook $20 for not wearing his army issue leggings. Patton is then summoned to a meeting with Air Marshal Coningham of the Royal Air Force, where he claims that the American defeat was caused by lack of air cover. Coningham promises Patton that he will see no more German aircraft - but seconds later the compound is strafed by Luftwaffe planes. Patton then defeats a German attack at the Battle of El Guettar; his aide Captain Jenson is killed in the battle, and is replaced by Lieutenant Colonel Codman. Patton is bitterly disappointed to learn that Erwin Rommel, Commander of the German-Italian Panzer Army, was on medical leave due to having diphtheria, but Codman reassures him that: "If you've defeated Rommel's plan, you've defeated Rommel".
After success in the North Africa campaign, Patton and Bernard Law Montgomery plan the Allied invasion of Sicily. Patton's proposal to land his Seventh Army in the northwest of the island with Montgomery in the South-East (therefore potentially trapping the German and Italian forces in a pincer movement), initially impresses their superior General Alexander, however Eisenhower rejects it in favour Montgomery's more cautious plan, which places Patton's army in the South-East, covering Montgomery's left flank. Whilst the landing is successful, the Allied forces become bogged down, causing Patton to defy orders and push his army northwest to Palermo, and then to the port of Messina in the northeast, narrowly beating Montgomery to the prize, although several thousand German and Italian troops are able to flee the island. Patton insists that his feud with Montgomery is down to the latter's determination to be the 'war-hero', and to deny the Americans any chance of glory. However, Patton's aggression does not sit well with his subordinates Bradley and Lucian Truscott.
Whilst on a visit to a Field Hospital where many American soldiers lie wounded or dead, Patton notices a soldier, shell-shocked and crying from nervousness from the fighting. Calling him a coward, Patton slaps the soldier and even threatens to shoot him, before demanding his immediate return to the frontline. Because of this, Patton is relieved of command and by order of Eisenhower, forced to apologise to the soldier and to the those present in the Field Hospital. Patton took it further by apologizing to his entire command.
Because of this, and for being too liberal to the press, Patton is sidelined during the D-Day landings in 1944. Instead, he is placed in command of the phantom First United States Army Group in southeast England as a decoy. German General Alfred Jodl (Richard MÃ¼nch) is convinced that Patton will lead the invasion of Europe.
After begging his former subordinate Bradley for a command before the war ends, Patton is placed under him in command of the Third Army and performs brilliantly by rapidly advancing through France, but his tanks are forced to a standstill after they run out of fuel - the supplies being given to Montgomery's bold Operation Market Garden, an airborne operation in the Netherlands, much to his fury. Later, during the Battle of the Bulge, Patton relieves the town of Bastogne and then smashes through the Siegfried Line and into Germany.
At a previous war-drive in Knutsford, England, General Patton had remarked that the United States and the United Kingdom would dominate the post-war world, viewed as an insult to the Russians. After Germany capitulates, Patton directly insults a Russian general at a post-war dinner; fortunately, the Russian insults Patton back, defusing the situation. Patton then makes an offhand remark comparing the Nazi Party to the political parties in the US. In the end, Patton's outspokenness loses him his command once again, though he is kept on to see to the rebuilding of Germany, with the disconcerting incident of a runaway ox-cart narrowly missing Patton foreshadowing the general's ignominious actual death in a car accident in December 1945.
The film ends with Patton walking his dog, a bull terrier named Willie, and Scott relating in a voice over that a returning hero of ancient Rome was honored with a triumph, a victory parade in which "a slave stood behind the conqueror, holding a golden crown, and whispering in his ear a warning: that all glory ... is fleeting."

Question: Why is Erwin Rommel on medical leave?
Answer: Diphtheria