I'm not really sure when the confleet would have been the largest, but part of me wants to say the pre-war fleet, as confed had numerous battlewagons and several carriers, although most were lost in the first days of the war. During the war, there seem to be few times when confleet has a large amount of capships, possibly prior to the mid-2660s battles which gutted half of confleets carriers or in the post-2667-68 right before the armistice because confleet had finally gained an edge and was about to commission several new heavy carriers, and was also still creating CVEs which were proving their weight in gold.