Rathatiratha-Sankhya Parva is the fifty ninth Upa parva included in the fifth Maha parva named as Udyoga parva. Vaishampayana continued narration to Janamejaya in reply to his queries as follows.
Immediately after the return of Uluka, Yudhishtira had opined with Drishtadyuma to be the Senapathi, means the commander for his leading active army. Drishtadyumna was given army camping order at his choice. Yudhishtira had announced Drona as his enemy target and had suggested to his other six commanders the various other enemy war targets. During the war, surrendering of enemies was the main aim but self-defense was inevitable. Killing was not desired from the side of Yudhishtira. Everybody on the side of Yudhishtira would follow war time rules. Each commanders would blow the conch to start or stop the war.
Why Yudhishtira allotted the seven commanders in chief with enemy targets?
The seven commanders on the side of Yudhishtira were assigned enemy targets on the co-option methods. Drishtadyuma had already got Drona as the opposite target of the war suggested by Yudhishtira. This process is called as Senapati Niyoga before starting the war. Shikhandi was assigned Bhishma. Sahadeva got Shakuni. The five Upapandavas, means the five sons of Draupadi were kept in the reserve against the five Trigarta Princes. Chekitana was against Shala. Shaibhya got Kritavarma. Arjuna got Karna. Bhima got Duryodhana. Abhimanyu was kept in reserve but arranged against Vrishasena and other strong kings since he was more able than his father Arjuna. These were flexible assignments; in the field, each and every fighting soldier has to face any kind of enemies who came in his front row. Drishtadyumna was free to lead in the war taking his own war-time decisions.
What information from Bhishma was desired by Duryodhana?
Duryodhana had already assigned Bhishma as the commander-in-chief for his army troops. Hence he desired to know from his open mouth and loud voice about the capabilities of his side, details of leading and succeeding soldiers. The army ranks were referred as Atirathas, Rathas and Ardha Rathas.