Because logic sees me through rough waters, that's how I know.
There was only one incursion into Confed space that we know of...the one through the Kilrah gate. Therefore, the force in SO was, in all likelihood, the stuff thrown through the Kilrah Gate when the cutscene camera wasn't looking.
The Kilrah Gate probably took a good amount of resources to make (like a dovin basal capable of performing a Ygrand's Core). Otherwise, the Nephilim would be opening gates all over the place. They tried constructing another gate underneath out noses, with their Stellar Accretion device at Proxima Centauri. Therefore, the one they did make, they'd make as large as they possibly could...or as large as they were willing.
Their main fleet was being lead by a Tiamat, which had to squeeze to make it though the gate. They probably don't have anything larger, and if they do, it's probably their flagship...something they didn't want to risk sending through the gate. Therefore, the Tiamats are probably either the largest or the second largest ships that they, er, grow...otherwise, they'd make the gate larger to accomodate them. And in the losing cutscene, they take a Tiamat to Earth...not something larger.
Maybe it was just a light recon...but I doubt it. You don't send some of your dreadnoughts on a RIF. This was the beachhead, to secure the front for the invasion...and they do invade, should you die or eject in the last mission of WCP.
[Edited by Nep Parth on 05-27-2001 at 21:37]