Rommel asked Hitler for command of a panzer division. On 6 February 1940, three months before the invasion of France, Rommel was given command of the 7th Panzer Division, for "Fall Gelb" ("Case Yellow"), the invasion of France and the Low Countries. Some other officers did not agree with his promotion. Rommel's initial request for command had been rejected by the Chief of Army Personnel, who cited his lack of previous experience with armoured units and his extensive prior experience in an Alpine unit made him a more suitable candidate to assume command of a mountain division that had recent need to fill its commanding-officer post. Rommel had, however, emphasized the use of mobile infantry and recognized the great usefulness of armoured forces in the Poland campaign. He set about learning and developing the techniques of armoured warfare with great enthusiasm. The decision to place him in command of an armoured division was borne out to be an excellent one. In May, 1940 his 7th Panzer Division became known as the "Ghost Division" because its rapid advances and fast-paced attacks often placed them so far forward that they were frequently out of communication with the rest of the German army.