Di Giussano Anti-Aircraft Cruiser Project

[Tzoli]

Saving this from the now defunct but still avaiable WOWs forums, an old 2015 post about the proposed AA cruiser conversion of the 4 Alberto Di Giussano class cruisers.

https://forum.worldofwarships.eu/topic/5736-the-di-giussano-aa-cruiser-project/

According to Franco and Valerio Gay in The Cruiser Bartolomeo Colleoni published by Conway Maritime Press, there were several conversion plans, drafted both by the Comitato Progetti Navi (the in-house navy design team) and O.T.O.

The first design was presented by Comitato Progetti Navi in February 1938, it involved the removal of all 152mm turrets to replace them with 16 single 90mm/48 (the gun was still under development at the time and it was somewhat shorter, L48 instead of L50) supplemented by ten twin 20mm machineguns amidships. It was a pretty simple conversion, fire control equipment was to be installed on the slightly modified bridge, while ammunition magazines and hoists would have been modified to handle 90mm and 20mm ammuntions. Around the area of the 90mm mounts the deck would have been reinforced with 30mm of nickel-chrome steel plates, improving horizontal protection. The removal of the 152mm turrets was estimated to compensate for the added weight of the armour plates and the new armaments.

It's the first drawing of this picture from a Russian book (click on the picture for full resolution):

Meanwhile in March 1938 O.T.O. presented its own design which had been required by the Navy ministry, this is the conversion of your picture where it says "marzo 1938" and the second drawing from the picture I posted above. It was a more radical affair, the arrangement of the 16 90mm guns was identical, but it involved the full reconstruction of the bridge, removal of the tetrapod mast and installation of four directors, this allowed to control independently each of the three groups of 90mm guns and the 20mm machineguns, with obvious advantages in handling contemporary multiple aerial threats. The same 20mm were concentrated on two elevated and stabilised platforms just forward the second funnel, this solution would have significantly improved their arcs and volume of fire compared to the solution proposed in the earlier proposal.

The final design is the hybrid one, it was presented by Comitato Progetti Navi in June 1938, I believe it kept in account the O.T.O. proposal because it's similar for some aspects, but I'm not sure about it. Four fore 90mm single mounts are gone in favour of two twin 135mm/45 O.T.O. mounts; fire control installation was modified to handle the new gun, with a 6m rangefinder and relevant fire control installations, while high angle directors for the 90mm guns would have been reduced to three. It's peculiar that the book of Franco and Valerio Gay insists, twice, that the 135mm guns and relevant modifications to the magazines were located aft, not fore, but I think it's a mistake.

Personally I always favoured the second proposal, reducing volume of AA fire for a weak anti-surface capability looks like a bad compromise to me. The conversion was not carried out apparently because the AA armament of the capital ships and accompanying escorts was perceived as adequate, while pre-war strategy never considered the need of protecting traffic to Libya. Also it seems that there were bottlenecks in the production of the new 90mm/50 guns.

EDIT:
A variation of the third proposal called for one single elevated platform with the 20mm machineguns disposed at arc like in the first proposal, I suppose this variation lacked the stabilisation of the O.T.O. proposal. It's the "variante al progetto giugno 1938" in your picture, but it's not very clear from the side view, I'm going to post the relevant pictures from Conway's book to better illustrate it:

 

[Phoenix_jz]

Personally I always favoured the second proposal, reducing volume of AA fire for a weak anti-surface capability looks like a bad compromise to me. The conversion was not carried out apparently because the AA armament of the capital ships and accompanying escorts was perceived as adequate, while pre-war strategy never considered the need of protecting traffic to Libya. Also it seems that there were bottlenecks in the production of the new 90mm/50 guns.

In regards to this specific project, this lack of emphasis on protecting convoy traffic wasn't really relevant - these ships were not intended for convoy escort, but rather as AA escorts for the fleet. For this reason, there was no effort to modify the machinery despite the potential benefits that could have come from removing some of the boilers (and utilizing the space for other purposes).

More consequential was the production bottlenecks around the gun systems in general. The studies for converting the Giussano-class into cruisers began in earnest in 1937. The decision to go ahead with the conversion of the Duilio-class battleships had been made at the start of the year (requiring 20x 90/50 and 20 quadraxial mounts and between the two ships, as well as 24x 135/45 in eight three-gun turrets) under the 1937/38 naval program. However, the 1938 supplemental program, approved in 1938, added another pair of Littorio-class battleships (24x 90/50 in 24 quadraxial mounts) and twelve of the Capitani Romani-class oceanic scouts (96x 135/45 in 48x two-gun turrets).

In light of this, the production backlogs for these guns and their mounts would be considerable for some time. To rebuild all four ships to either MARICOMINAV's or OTO's initial configurations required 64x 90mm guns and an equal number of turrets - almost equal to all the 90/50 installations for the Italian battleship program (68 mounts on six ships). MARICOMINAV's revised design from June reduced the requirement to 'only' 48 mounts of the 90mm, while adding a requirement of 16x 135/45 in eight two-gun mounts, but this was still a very large ask for what was meant to be a short term program, given Italian industry would be occupied with the battleships and oceanic scouts in the meantime (1938 to 1942).

In the longer-term (1942 and beyond), there would likely be more room for such a program, though by that point at time they likely would have been looking on to later gun systems.

 

[Tzoli]

Indeed the 90mm/50 Ansaldo and OTO guns were much better oriented against AA warfare then to anti surface warfare, not really a DP weapon though it is capable of such action.
The RM really liked this weapon as in 1942 the conversion proposal of the heavy cruiser Bolzano into a sort of catapult ship / AA cruiser too featured 10 such guns!

But another AA cruiser project based on the old Ancona (Ex SMS Graudenz) cruiser in 1936 featured 13 twin 100mm guns rather the single 90mm ones though at this time the 90mm might be only in theory phase.

And lastly I've recently heard of another AA cruiser project of the Regia Marina the cruiser Bari (Ex SMS Pillau)
First posted here:

All the World's Battlecruisers-Italian cruiser Bari conversion to an AA cruiser.

I read that this ship was planned to be converted to an AA cruiser in 1943 with 6-90mm guns. Does anyone have a drawing of this? Thanks, Dave G

www.tapatalk.com

Than an Italian friend of mine found this on a different forum:
https://www.aidmen.it/forums/topic/973- ... capa-flow/

Nel 1943 ne venne prevista la trasformazione in navi antiaeree. I lavori iniziarono a Livorno sul BARI, che avrebbe dovuto ricevere 8 cannoni aa da 90/50 mm, 8 x 37/54 mm e 8 x 20 mm, ma la nave venne affondata in porto durante un bombardamento aereo alleato il 28 giugno 1943 prima che i lavori fossero stati completati. Se ne avviò il recupero, interrotto dall'armistizio dell'8 settembre, quando il relitto venne sabotato. Il relitto fu parzialmente smantellato dai tedeschi durante il primo semestre del 1944, poi nel dopoguerra venne recuperato il 13 gennaio 1948 e demolito.

In 1943 it was planned to convert them into anti-aircraft ships. Work began in Livorno on the BARI, which was to receive 8 x 90/50 mm, 8 x 37/54 mm and 8 x 20 mm AA guns, but the ship was sunk in port during an Allied air raid on 28 June 1943 before the work was completed. Salvage was started, but was interrupted by the armistice of 8 September, when the wreck was sabotaged. The wreck was partially dismantled by the Germans during the first half of 1944, then after the war it was salvaged on 13 January 1948 and demolished.

 

[Dilandu]

Personally I always favoured the second proposal, reducing volume of AA fire for a weak anti-surface capability looks like a bad compromise to me.

Weren't a dual-purpose version of 135-mm guns being designed durig the war? If I recall correctly, it was eventually implemented as basic for "Guiseppe Garibaldi" dual-purpose mount during her 1950s missile refit.

 

[mirco1961]

Weren't a dual-purpose version of 135-mm guns being designed durig the war? If I recall correctly, it was eventually implemented as basic for "Guiseppe Garibaldi" dual-purpose mount during her 1950s missile refit.

No: the Garibaldi Turret project is of 1957

 

[Dilandu]

No: the Garibaldi Turret project is of 1957

Hm. So it wasn't based on previous wartime efforts? I recall that 135-mm DP mounts were planned for repurposed Siamese cruisers, so at least some work apparently was done on them?

 

[Phoenix_jz]

Very little information exists on the WWII effort to turn the 135/45 into a DP gun, unfortunately. The obvious move would have been to increase the maximum elevation beyond +45°, but nothing can confidently be said beyond that.

Though I would guess that part of the effort might be the installation of a powered rammer or improved recoil rammer, as the one originally installed on the gun system was to weak to operate automatically beyond elevations of +30°, and likely lead to the commonly reported lower rate of fire of 6 rpm. The recent Storia Militare Briefing on the Capitani Romani-class noted that the rate of fire actually was as high as 8-10 rpm per gun, not the 6-7 commonly reported - the lower rate of fire reflects a more realistic figure commonly seen in service.

The 135/45 M1957, meanwhile, is a different project using entirely new turrets. It was a semi-automatic gun system that had similar ballistic performance to the original gun system, but had a much higher rate of fire - 20 rpm per gun.

But another AA cruiser project based on the old Ancona (Ex SMS Graudenz) cruiser in 1936 featured 13 twin 100mm guns rather the single 90mm ones though at this time the 90mm might be only in theory phase.

Indeed - 1936 is the crossover year for these guns - effectively every major project up to 1936 used tee 100/47 as their heavy AA gun system. 1936 is the year the 90/50 starts being introduced to all the cruiser and battleship projects ongoing that could support it (including the Littorio-class, who up to that point were also to be equipped with 100/47's).

 

[Dilandu]

The 135/45 M1957, meanwhile, is a different project using entirely new turrets. It was a semi-automatic gun system that had similar ballistic performance to the original gun system, but had a much higher rate of fire - 20 rpm per gun.

Thank you for clarification!

 

[mirco1961]

Hm. So it wasn't based on previous wartime efforts? I recall that 135-mm DP mounts were planned for repurposed Siamese cruisers, so at least some work apparently was done on them?

no, Taskin cruisers will have Bofors 15 cm/53 (5.9"), the 'Etna Class' conversion will have a slighty modified version of the turrets of the Capitani Romani class.