baptism by fire
1. The first time a soldier enters combat. Taken from a phrase that originates from the Bible, in Matthew 3:11. As they marched onto the battlefield, you could see all of the uniformed boys become men as they experienced baptism by fire.
2. A difficult ordeal that one has to undergo through immersion and without preparation. One week into her new job, Mary felt like she was undergoing a baptism by fire when she was suddenly put in charge of the company's largest account.