If my ever fading memory recalls, the first attempt at torpedoing with the B-26 was at Battle of Midway and it was a failure.
Partially correct. There are only two instances the USAAF used B-26s as a torpedo bomber and both actions occured on the same day. While the B-26 torpedo bombers were attacking the IJN fleet off Midway, another group of B-26 torpedo bombers were attacking the IJN carrier Ryujo off the Aleutians. In both attacks, the B-26s suffered heavy losses and didn't hit anything.
ack-ack