Because New London is so far away from Des Moines, we recommend simply booking a flight. Other options to New London do exist, but going by plane will save you valuable time. Book as soon as you can, as there may be limited availability.
For these medium length trips, it's important to book your tickets as soon as possible. While there are bus or by car transportation options available, the sooner to book the better. While prices for buses or trains might not fluctuate as much as flights, their availability certainly will. It's recommended to book these flights at least 2 weeks away, but even more if you are able.