In 2240, Sinclair was promoted to fighter pilot, continuing a Sinclair family tradition that had extended as far back as the Battle of Britain. Less than a year later, Sinclair was promoted to squadron leader; due to his rapid rise through the ranks, the rumor of the day was that Sinclair was on the fast track to making Admiral. As squadron leader, Sinclair fought at the Battle of the Line, the last major battle in the Earth-Minbari War. During the course of the battle, his squadron was destroyed by the Minbari, and his fighter was badly damaged. In a last act of defiance, Sinclair attempted to ram one of the Minbari cruisers. He failed in this when he was captured by another Minbari cruiser for interrogation by the Grey Council. The Council's Triluminary detected Valen's DNA in Sinclair, so they assumed, to their profound shock, that he possessed the soul of Valen, a hero of the Minbari who led them to victory 1,000 years ago against the Shadows. It was concluded by the Grey Council that Minbari souls were being born into human bodies. The discovery of what Sinclair possessed led the Minbari to surrender and return Sinclair to his fighter, the memory of his time aboard the Minbari cruiser blocked (though this block would not be permanent and would break down years later). Sinclair — and the Earth Alliance — believed that he had blacked out from the acceleration. When Babylon 5 was brought into operation in 2257, Sinclair was selected by the Minbari to command the newly constructed station. He was selected over many more senior officers, including Colonel Ari Ben Zayn, all of whom had been vetoed by the Minbari (they had stipulated that they should approve the choice of Station Commander, as they had shared the cost of construction).