This paper describes an ultra-high-vacuum (UHV) chamber for environmental fatigue crack growth tests. The main components of this testing device are the working chamber, where the test is conducted, the gas entry lines, and the quadrupole chamber, which is used for analyzing the environment. Advice on the assembly and behavior of these components is also given. As an example of the performance of the system, novel results are reported of crack growth rates in an aluminum alloy (AA7017-T651) when tested in high vacuum, pure oxygen, and at different water vapor pressures.