First Division

The First Division (一番隊, ichibantai), also known as Squad 1 in the English Dub, is one of the Gotei 13, headed by Captain Genryūsai Shigekuni Yamamoto.
The 1st Division follows the traditional organization of a Gotei 13 Division.
No special duties have been noted for the 1st Division. The First Division is ranked highest among the 13 Divisions. Even subordinate members of the First Division are considered model Shinigami. Emergency must be dealt with swiftly; quick decisions and quick actions are essential. The division is able to ascertain a situation and mobilize quickly even before an order is issued. That is the true value of the First Division.
Like all the other barracks, the 1st Division Barracks house the offices and living quarters of the Shinigami of the 1st. In addition, due to the 1st Division being the division of the Captain-Commander, the barracks hosts the assembly hall where the captains gather for their meeting. The barracks also has a room set aside for lieutenants' meeting. Captain-Commander Yamamoto's office within the barracks commands a wide, sweeping view of Seireitei.

Info from :  http://bleach.wikia.com/