From: PDX (and now) London, UK
There are a confusing number of units that have CD guns for the Japanese. It can be confusing.
The most easy to find are the large numbered base force units. 1st Base Force for example, that come with 8 x 12cm 10YT DP and 16 x 8cm T88 DP guns. These will fire and do some decent damage to an ill-prepared invasion. If I remember correctly the DP guns come as an upgrade, or maybe just for some of the base forces. They're also a good addition to AA defences, these DPs being some of the better Japanese AA gun types.
The better units are all of different types and make-ups, and as Loka and others have said, often need to be combined. The Wake CD gun unit is the most obvious, and arrives intact.
Wake CD gun Bn - This one gets 20cm and 15cm CD guns plus 12cm CD and DP guns and some 8cm DP guns.
Kure 7th SNLF - a Naval Infantry unit - 8 x 12cm 10YT DP and 16 x 8cm T88 DP guns
Combined 8th SNLF - a CD gun unit. This one gets 14cm CD plus 12cm CD guns, 12cm DP and some 8cm DP guns when combining two units (a port unit and an SNLF).
3rd Special Base Force - an Engineer unit (Base Force) This one gets 20cm and 14cm CD guns plus 12.7cm DP and some 8cm DP guns in an upgrade.
31st Special Base Force - an Engineer unit (Base Force) This one gets 15cm CD guns plus 12.7cm DP, 12cm DP and some 8cm DP guns in an upgrade.
(These two are the only Special Base Force to get this CD gun addition. All others only get 4 x 8cm DP guns only).
There are a few other smaller mobile units, including some Naval Guards that arrive late on small islands around Japan and have 6 x 8cm DP guns.
Being different unit types the may behave slightly differently in certain situations, like reacting to and firing on a bombardment TF or firing at passing ships. I think only the CD gun types will fire in a strait at passing ships, but may be wrong on that.
Forgot to add another one that shows up in mid-44 on Iwo. The Iwo-Jima naval guard unit has 12cm and 8cm guns. There are a lot of these guard units showing up with the 8cm DP only, but this one includes the bigger guns, cruisers beware.
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