Did you or will you have your baby take swim lessons, do they really learn how to swim in just 4 hours? Really?

my son is 7 months old, the next swim lesson cl will be in april he will be 9 months old, it's from 6-6:30 p. 2 days a week for 4 weeks. that's 4 hours, they really can learn to swim in four hours? how did your baby like the cles, i'm a little nervous i'm petrified of water so i hope i don't have to get in there with him. so i'm wondering if anyone else has or will be having their baby's take swim lessons. and at what age. i know i'm late starting, but their last cl he was only 6 weeks old, thank you and have a great week.