Apollo 9 was the first Apollo mission to use a lunar module in a crewed mission.
Launched on March 3, 1969, Apollo 9 tested the complete command-and-service-module and lunar-module combination in Earth orbit. Commander James McDivitt, command module pilot David Scott, and lunar module pilot Rusty Schweickart practiced procedures that would later be required for a lunar landing.
The lunar module Spider separated from the command module Gumdrop and performed independent maneuvers. Schweickart and McDivitt also tested the portable life-support system that astronauts would use while walking on the Moon. These tests were essential because the lunar module had never before carried people.
Apollo 10 followed with a full dress rehearsal in lunar orbit, taking its lunar module close to the surface without landing. Apollo 11 then used the experience from both missions to attempt the first crewed lunar landing.