On the 15th of December Banks took the command of the Department of the Gulf, although the formal orders were not issued until the 17th. The officers of the department, as well as of the personal staff of General Butler, were relieved from duty and permitted to accompany him to the North. The new staff of the department included Lieutenant-Colonel Richard B. Irwin, Assistant Adjutant-General; Lieutenant-Colonel William S. Abert, Assistant Inspector-General; Major G. Norman Lieber, Judge-Advocate; Colonel Samuel B. Holabird, Chief Quartermaster; Colonel Edward G. Beckwith, Chief Commissary of Subsistence; Surgeon Richard H. Alexander, Medical Director; Major David C. Houston, Chief Engineer; Captain Henry L. Abbot, Chief of Topographical Engineers; First-Lieutenant Richard M. Hill, Chief of Ordnance; Captain Richard Arnold, Chief of Artillery; Captain William W. Rowley, Chief Signal Officer. Banks's orders from the government were to go up the Mississippi and open the river, in co-operation with McClernand's expedition against Vicksburg. "As the ranking general of the Southwest," Halleck's orders proceeded, "you are authorized to assume control of any military forces from the upper Mississippi which may come within your command. The line of the division between your department and that of Major-General Grant is, therefore, left undecided for the present, and you will exercise superior authority as far north as you may ascend the river. The President regards the opening of the Mississippi river as the first and most important of all our military and naval operations, and it is hoped that you will not lose a moment in accomplishing it." Immediately on assuming command Banks ordered Grover to take all the troops that were in condition for service at once to Baton Rouge, under the protection of the fleet, and there disembark and go into camp. Augur was specially charged with the arrangements for the despatch of the troops from New Orleans. Before starting they were carefully inspected, and all that were found to be affected with disease of a contagious or infectious character were sent ashore and isolated.