That is true. Yamamoto, as well as the entire naval officer corp, was against the war with the West. When the Imperial Navy was founded, the Empire based the Navy on British model; the Army was based on first the French, then Prussian/German model. The Navy always had affinity towards Britain and by extension the US, from which countries much of the Naval technology was acquired. Because the Japanese government was run by the Army, the Navy had little influence into Japanese foreign policy.

There is an interesting story regarding Yamamoto and Tojo. Apparently, during a cabinet meeting, Yamamoto kicked Tojo's chair out from under him. The hostility between the Army and the Navy likely caused much of the operational disasters during the Pacific War.

The Pearl Harbor attack was designed with ending the war with one massive strike. It was Japan's Schlieffen plan, but Nagumo, being a cautious man, did not comprehend the purpose of the operation. He withdrew premateurly, fearing loss of his carrier group, not realizing that Yamamoto planned to end the war with this one strike. Yamamoto gambled the war at the risk of his entire carrier group; if the appointed operational chief were the daring Yagamuchi, the Pacific War may have progressed differently.