Reading today about Anzio and the complexity of some of the behind the scenes machinations gives new insight into the extensive planning which goes into implementing any operation of war.
General Eisenhower had approached General Patton about going in to clean up the mess at Anzio. Patton was delighted to accept. Then as quickly as Eisenhower had offered, he then withdrew the offer. Supposedly Patton never learned why the Anzio command offer was withdrawn. The reason Patton was not sent to Anzio was due to the presence of Lt. General Truscott.
Lt. Gen. Lucian K. Truscott was someone Eisenhower had wanted sent to England to help in the invasion at Normandy. When General Mark Clark became Commander of the Allied Army Group, Truscott then assumed command of the Fifth Army.
Senior officers on both sides wanted Patton at Anzio. British Admiral Sir John Cunningham wrote the First Sea Lord "It's a thousand pities we didn't let Patton do the job!"
Patton: A Genius for War
I just posted a little more background information here.
I think what goofed things up was Clark telling Lucas to be cautious on D-Day off the record at the time. That he had authorization to do what he wanted but to be careful. Lucas took it literally.