: Just wondering if it was rather referring to the moon that they turned into
: the Marathon, instead of Earth's moon?
That seems rather unlikely - if you were going to refer to Deimos, you would say 'Deimos'. Likewise, if you were going to refer to the Moon, you would say 'the Moon'. It's possible, but I doubt it.
I always thought he was referring to some form of Jjaro tech that the UESC uncovered. Given the similarity between Pfhor and Jjaro tech (the Pfhor did borrow a lot of their shtuff from the Forerunn-- err, I mean Jjaro), one can guess that Durandal believed the distant Pfhor ships were in fact Jjaro ships. This would certainly explain his interest in leading them to Tau Ceti, and if I recall there was some hint that Durandal was surprised to some extent by the hostility of the Pfhor, though of course in the end it did not matter as he was able to turn the situation to his advantage with our help.
Vale,
Perseus
