Shipbucket

So, I was looking into the interwar designs of some navies.

I noticed that they have a number of them - like Argentine cruisers or Finnish coastal defense ships - carries medium-caliber DP i.e. heavy AA guns, mostly around 3-4 inches.

Now I wonder what kind of fire control they have for those guns

I can't find any information on their AA director nor associated systems...but I feel that it's very unlikely that the major powers would be happy to supply those to them.

I mean, even immediately prior to the war, Brits' HACS/FKC were perhaps most common state of the art equipment, US just introduced Mk37 and its computer following the Mk33, KM did have a number of directors for 88 but I'm not sure if they provide automatic gun laying on anything but capital ships, Japan doesn't even have dedicated ones until late in the war...I don't know about Italian ships.

If there was no HA/AA director let alone computerized/automatic one, I wonder how did they set fuzes or achieve barrage fires?? Using the surface-fire rangefinder? Did Japan originally fire theirs like that too?

They were probably not that far off the usual standard of most cruisers of the time to be honest, as you point out even systems like HACS and Mk37 did not appear in numbers until the late 1930s. Basic predictive fire control tables would have been used, little advanced from such equipment of the Great War but probably adequate against the likely relatively slow biplane threat of the early 1930s.

The Italian-built de Mayo-class cruisers for Argentina have a secondary rangefinder aft that was probably used for some measure of AA control in conjunction with sights on the guns themselves. They were built in the late 1920s - when such equipment was rare on cruisers, although they actually have a heavy AA armament (6x2 4in & 6x1 40mm pom-poms) compared to cruisers in even major navies of the time. The La Argentina built in the late 1930s doesn't have any HACS system, but there seems to be a HA rangefinder perched atop the main director tower. Notably the AA armament is much lighter however; 4x1 4in & 6x2 1in Vickers MGs (later replaced by 8x1 2pdr pom-poms).

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