|The following is based on pre-release information for the canceled Fallout Online game by Interplay Entertainment (Codenamed Project V13) and is not considered canon.|
We have the information, but they have the area knowledge. Work with them. Make bridges.”— Elder Francis
Despite the Guardian Brotherhood being on barley tolerant terms with the Brotherhood of Steel they were not above cooperating when it came to a common goal. Elder Francis of the Brotherhood of Steel was eager to build bridges with the Guardian Brotherhood, and was on stable enough grounds to assign training missions with them.
The Guardians took part in a mission to find out if there truly is a tunnel entrance to the Glow which entailed a beach assault working with a Brotherhood of Steel squad dubbed the "Brothers Grimm" by the Guardians because of the tall tales they would spin.
The Guardians squad practices differed from the Brotherhoods in that they used minimal communication on the field, barley any words, or even hand gestures, which Miller, a Brotherhood scribe, found impressive and felt was something to report back to Elder Francis.
The outcome of the mission was never revealed.
The Guardian Brotherhood appears in the short story "On the Beach", published in The Armageddon Rag, Vol. 3. They would have likely appeared in Interplay's original Project V13, also known as Fallout Online. This project has been cancelled in favor of a new, unrelated, Project V13.