I dunno either, Peridixion!
That's just what Mr. Yoshimoto calls it. Actually, in the Japanese text it says: "2A3/#12467;#12531;#12487;#12531;#12469;#12488;#12540;2P 406mm"
(can ya'll see that?), or: 2A3/ Kondensato 2P 406mm."
"Kondensato" is from the Japanese Katakana, so I have no idea of the actual spelling.
But what a big gun!