Overview
A possible fix for users who experience a black screen when they try and start the game.
Issue
If your game fails to launch correctly, and experience a hang on a black screen when you try and launch on Windows 10 (potentially others, but I can only speak to my experience), the following fix may work for you.
Fix
Navigate to the WindowsSysWOW64 folder, and copy “d3d9.dll” and “d3d9on12.dll” to your Silent Hunter IV root directory.
That’s all! Hope it resolves your issue.
As for why this fixes the problem, your guess is as good as mine. My guess is that the .DLLs carried by Windows are more up-to-date than the ones carried in the SH4 Steam distribution, and at some point since Steam last updated, those DLLs have become incompatible with Windows.