Decoy Question
 

When did decoys (Bold I believe) become historically available in WWII ? and when is it available in the game, I have gone to the Chief engineer and brout up the maneuvers screen only to find that the decoy is greyed out (it's 1940) I have also found this in some of the single missions in the game.

Thanks.

I don't know when they're available in the game, but click on the "?" in the U-boat upgrade screen when in port and you can see a timeline of all available equipment and technology upgrades.

The Bold became available in Late 1943, but wasn't ready to common active duty before 1944