I echo what jimmbo said. It took a lot of tries to make those early rockets even semi stable. So many exploded on the pad or right after takeoff. Those guys had titanium cojones, alright.
Glenn was a class act and a wonderful example for the U.S. I was 9 or 10 years old when the space race went into full swing. It was an incredibly exciting time, when the country had a sense of purpose. Anything was possible, and Glenn and his co-adventurers personified the can-do attitude this nation had back then.
RIP, John Glenn. Thanks for everything.