HMS Effingham as AA cruiser

[tigercat]

 Firstly and obviously she isn't sunk off Norway.

She already differed from her sisters in that she was rebuilt with a single funnel and 9 single 6 inch presumably from the C class when they were converted

http://www.the-blueprints.com/blueprints/ships/cruisers-uk/8451/view/hms_effingham_(1940)/

the 6 superimposed mounts are replaced with 4.5 inch guns QF Mark I in twin mounting UD Mark III as found in HMS Scylla

The Beam guns and catapault crane etc along with the 4 in guns are replaced with ligh AA Oerlikons, Bofors, 20 mm etc

I'm not too sure whether this would work but there's a possibility the aftermost  6 in gun position could be replaced with another turret

This gives her 12 - 14  4.5 inch 

[rickshaw]

Might have stability problems with all that extra weight topside.   Whats the difference in weight between the two guns and mountings? The single 6 inch versus the twin 4.7 HA mounting?   Then there may be problems with the ammunition handling and supply.  For AA work you need a significantly higher ammunition handling rate and a much larger magazine.  Removal of the rear 6 inch would be sensible - having mixed gun types complicates resupply.  Removal of the aircraft hangar and catapult would save some weight and would free up deck space for more light AA.

[tigercat]

6 inch single  mount

CPXIII, XIII* and XIII**:  14.5 - 14.8 tons (14.7 - 15.1 mt)


4.5 inch

Twin Mounts
   Mark II BD:  37.95 tons (28.56 mt)

so 9 x 6 inch = 133 tons
6 twin 4.5  turrets = 227 tons

so about an extra 100 tons

alternatively a simiar outfit to HMS Delhi

6x 5"/38  at 18 tons each 108 tons

[tigercat]

Someone in the Admiralty obviously had a similar idea. Thats a lot of Oerlikons  for 1940 it looks like they were thinking  of maybe converting her to the AA role   

In November 1930 Frobisher was reduced to reserve before being converted to a Cadet's Training Ship, in which role she served from 1932 until 1939. She was laid up in early 1939, until the outbreak of the Second World War. In January 1940 Frobisher started an extensive refit, that rearmed her with five 7.5 inch, and five 4-inch (102 mm) guns, and quadruple 2 pounder pom-pom and 19 20 mm Oerlikons.