[Bilge_Rat]

Radar - based on my reading, Samuel Morison's History of U.S. naval operations in ww2 and Clay Blair's Silent Victory, IJN ships never carried an effective radar, certainly not one that ever had any practical effect in any battle, does anyone one have solid evidence to the contrary?

Depth Charges - as Redwine pointed out, the IJN never developped heavy depth charges like the allies.

ASW capabilities - If you read through the documented encounters between the IJN and U.S. subs troughout the war, the IJN was at it's most effective at the beginning of the war. All their destroyers were equipped with sonar and they knew how to use it. However, from my reading it appears they never developped the team tactics used by allied escort, rather each escort would attack on its own. The IJN ASW effort became progressively worse as the war wore on and the crews became greener.

U.S. intel - The U.S. Navy broke the japanese codes before the war and were reading japanese messages throughout the war. They kept close track of the movements of japanese ships and U.S. subs were often dispatched to intercept specific warships or convoys, so the superb intel we get in SH4 is based on fact, although it may require some tweaking.

RDF - The japanese had a very effective Radio Detection Finding network set up before the war which allowed them to keep close tab on allied warships. The U.S. knew this from intercepted messages, which is why U.S. subs used their radios sparingly, although I don't know how this could be integrated in the game.