Quote:
is it known specifically which Yugumo units were completed with the larger bridge structures negating the need for the separate radar room below the main bridge?
Yes. Okinami, Kishinami, Asashimo, Hayashimo, Akishimo, Kiyoshimo. They were a second batch, construction for which began in the latter half of 1943.
If you are thinking about doing a late war version using the new Hasegawa kit, it may pay to wait a bit. The late war sprues set up suggests such a release at some point, as all is needed is the late war bridge. Hasegawa released its original DDs in sets of three different fits, so it makes perfect sense for them to do it again. Assuming they do, then Asashimo and Akishimo were both Fujinagata built, and would show the kit version of the degaussing cable.
Quote:
Was the separate radar room present only on as-completed units such as Hayanami or would earlier units like Naganami also receive that feature when updated with the type22 radar and new mast?
The earlier units were retrofitted sometime in mid 1943 - early 1944. It's possible that Suzunami and Onami did not survive long enough to get the radar upgrades.
Quote:
Also, with respect to intra-war updates: were roll-off DC racks, additional AA bandstands, and radars all applied in the same refit or performed piece-meal as the war progressed?
While I'm sure the preference was to do a comprehensive refit, I would think that piecemeal was more likely, particularly as it applied to the Type 22 radars. Type 22 radar production was spotty, so often ships got the foremast upgrade but had to wait for the radars. The Kageros are better documented in this regard. Yukikaze clearly got the mast upgrade before the actual unit was installed (her appearance in this fit at the Battle of Kolombangara was photographed afterwards at Rabaul). Isokaze has been documented as well in series of radio decrypts by Ultra.