Two types of rockets were used for Project Mercury. The first two of the six flights with an astronaut on board used a Redstone rocket. The four manned flights that orbited Earth used an Atlas rocket. Both of these rockets were originally designed as missiles for the United States military.
The project was named Mercury after a Roman god who was very fast. Each astronaut named his spacecraft. Alan Shepard included a 7 in the name of his Mercury capsule. This was because it was the seventh one made. The other astronauts included a 7 also. This was in honor of the seven astronauts chosen for the project.