Shipbucket

Nice work with these DD, give me inspiration for creating a design based on F-Class DD for RHN AU. And a question about guns: What is the relation between the 4.7" HE proposed by Krakatoa for my CAA Smyrni-with 75 degrees elevation and these 4.7" above? A joint program with Admiralty could perhaps work, including also the modified F destroyer (and a modified A-Class precceded the "F-HL"). A joint program could also cut something from developing time.

The Admiralty did consider the need for a 70degree elevation twin mount in the 1930s, but concluded that because of its size and weight it could only be effective on ships larger than destroyers, which were too lively. They still wanted destroyers to be around 1500tons, partly because of treaty restrictions, partly costs to build sufficient numbers, partly simply size to keep silhouette small for effective torpedo and night attacks.
On the gun front, the RN 4.5 began life as a 4.7 variant. The shell was redesigned to be heavier but more streamlined, and made as a fixed round to keep rate of fire high. That fixed round was too heavy to be loaded by hand on a small lively destroyer, and even when a separate charge version was developed for the Battle class, the ship needed was 2300 or 2400tons, a role change to fleet AA escort rather than a 1930s destroyer.
A destroyer's contribution then (Tribal at first, which were intended to take on some cruiser functions to offset the drastic shortage of cruisers) was to barrage fire, for which 45 or 55 (L,M) degree elevation was enough, but those classes and the later Battles were 2000ton ships. Direct firing at individual aircraft targets with medium calibre guns was largely ineffective until the VT or proximity fuze was introduced, not really foreseeable in 1935.
When considering whether a heavy AA mount will fit a small ship, things to remember are that some form of HA director is needed; it's topweight and stability that matter, not simply size of mounting; you need magazine space for enough ammunition. Firing at fast-moving aircraft uses a lot. It may be better to use the weight and space available for an effective short-range weapon like the pompom, remembering that you still need the medium calibre guns to fire at ships.
What about a 'light Battle' with two twin 45deg 4.7in forward and two or three twin Bofors 40mm as fitted by White's to Grom? RN could have had those on 1500 or 1600 tons in the late 1930s instead of JKN classes.

Added HMS Hotspur to first post on page one.

So the 4.7" HA was intended for larger ships. Could these two guns (the HA and yours on I,H,J mod have anything common? If deveolped paralel, could your 4.7" used on a modified F-Class and the HA available in 1936-37?

Odysseus,

The 4.7" HA is supposed to be available from 1935-36 in both single shielded and twin turret mountings. This is to be a new mounting, not the same as the one on the Nelsons. The singles could be retrofitted to the older A-G class or fitted to new builds of A-G type for export. Example would be the 'H' class order placed by Brazil. I have not drawn the single yet. I would think it would look similar to the mounting on the later T-Z class DD's.

Very nice work, I'm not going to get bogged down in the complicated world of RN destroyer mounts, but the designs look good.
This seems one of the most plausible ideas I've come across for some time. Of course, the Admiralty would probably want six guns to match the Fubuki's five but all ahead would be the best layout and the aft guns were probably able to be sacrificed. I guess the Admiralty would have favoured the pom-pom for standardisation and its supposed anti-MTB qualities, but from 1938 onwards the Bofors could have been considered much more seriously.

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Nice, so I can use the 4.7" HA to light cruisers from mid 1930's and perhaps retrofit to older designs (both local and british built turrets). A mod and F mod had the single mounting, CL and CA the double mounting.

The light Battle seem good idea. But RHN had focused to JKN and A mod, for maximum possible commonality between its DD. When I could have ASDIC in service;