In which mission it happened?
Design the H-class
How much time passed since start of mission?
Not much, first ranging shot were just fired.
How many other missions were played before crashing?
4, I played both ironclad missions twice.
How many ships were engaged for you and enemy (Many/Few/A specific nbr. if you remember)?
Only the battleships were engaging.
What was the distance between engaging ships (close/medium/long range)?
Long range.
Which speed boost you used?
x10
Were there a lot of gun shootings, or few (e.g all main guns firing plus secondaries)?
main guns (17"triple), secondairy, (8"triple and 5"triple)
Have you ever experienced this error-message outside of a mission? If yes, where (Main Menu, Custom Battle etc.)?
Nope.