I use KM40s on both my H-39 and AD (the front mounts) and it is very effective. I
am currently using the 4.1s on my Moltke, because while the rate of fire is lower
than the 3.46s, the extra damage is worth it against high level fighter (bombers and
scouts are really not a problem). Golden angle on the 4.1 and KM40s (5") are 32
with 12 being sea level. The next increments I use are 19, 22 and 27/28 this will
pretty much clear the sky at most levels. The worst are those CV drivers where they
constantly vary the height/altitude their fighters. Not only are they fast and tough
to track, and take
more than 1 shell to shoot down but now they are bounching around... Still it
usually isn't a problem to get 4000 points off AA in a typical battle. (My high I think is
in the 25K range....)

One comment. I always used 32 degrees on the KM40s. But with the 4.1" guns I
have started using 33 degrees with some success.

The 105mm (4.1 in) and 128mm (5 in) are supposed to have the same firing angle
(GA or golden angle) which is, in my experience, not true, thus allowing them to
be used in tandem in ships with uneven space in T mounts (think H39). The GA
for these two guns is 32 degrees.

Also, although the 105mm is "smaller" than the 128mm, the former weighs more than
the latter. Their rate of fire is, nevertheless, the same (1.2 sec)

In general: the 88mm (3.46 in) is a good option for Endem and other small ships
CL & CA). It is faster firing (0.80 sec) but shorter ranged. Its GA is 36 degrees.
The 105mm and 128mm are for BBs mainly due to weight and space restriction.

Of the three, the best gun is the 128mm KM40. Use when you can.

The AA for KM tends to depend on the ship.

3.46
4.1
or KM40s

3.46 and 4.1 are used on smaller ships that have weight/space restrictions and the km40s
work for H44 up.