PDU ON, SC 1
At start of campaign, I produce Ki57 I Topsy using Ha-5 engine pool...
When engine pool is exhausted, I don t upgrade to Ki 57 II Topsy, Ha-31 engine, as it is very similar to Ki-57 I Topsy, keeping Ha-31 production low only for Ki-46 II Dinah
There are enough engines in the pool to build out your DinahII's and Dinah III changes engines in 12/42.
So, early march 42, having most of my IJA transport squadrons equipped with Topsy and 30+ in reserve, I switch production to Ki-32 Mary , using Early Kawasaki engine with 80+ in pool...
Ki-32 Mary is much better than Ki-51 Sonia and can be also used for ASW despite short legs, but with its 250 kgs bomb, it can be a sub killer if something came close enough...
Skip building IJA light bombers completely and upgrade them to Ki-45's when those become available. Ki-45's are superior in range, bomb load, survivability (armor and durability), speed, etc. to all IJA light bombers. Only the Ki-48 has an advantage over it (range). It can also double as a heavy CAP fighter with appropriate pilots.
I resume IJA transport production with Ki-49 K Helen mid 43 which has much greater capacity than Topsy.
Because of the way that transport aircraft are handled, the capacity is the same. Transport aircraft transport max load / 2000. Fractions are ignored and only the whole number is used. There is also a minimum moved of 1 supply.
Ki-49-II KAI max load = 3500/2000 = 1.75, moves 1 supply.
Ki-54c max load = 1058/2000 = ~0.5 = minimum of 1.
Both will deliver 1 supply per mission.
See michaelm's post at http://www.matrixgames.com/forums/tm.asp?m=2483507
Your only concern with IJA transports are
1) How far can you send it? (Note: 50% of ferry range is max range for base to base supply delivery)
2) How many and what engines does it use? (production management)
3) Is is significantly more durable / ammored? (reduced operational losses)