If flying around at 300 KIAS, wasn’t difficult or challenging enough, they put you under a curtain, or hood as it was called, and you had to simulate being in the weather for learning how to navigate and fly solely on the aircrafts instruments.
Yes, in T-37 instrument training, we used to wear a bonnet over our helmet. It was helpful to shade and obscure the vision beyond the cockpit. Of course, it wasn’t as thorough as the hood, because you have to position the bonnet just right so that you couldn’t see beyond the cockpit. In essence, the honor system was the rule of the day, because with the bonnet, you could get frustrated to the point that you would want to take a peek beyond the cockpit instruments to see where you needed to be flying. Of course, that would defeat its purpose, and you wouldn’t be getting quality training. Also, you were training for real life circumstances; and if you were not disciplined, you could find yourself one day facing true instrument conditions and you couldn’t perform properly. That could lead to tragedy.