What was the cause of the fire in the RC-135V rear cabin?

The cause of the fire in the RC-135V rear cabin was due to the failure to tighten an oxygen fitting. When oxygen fittings are not secured properly, they can lead to leaks. Oxygen is highly flammable, and even a small spark or ignition source can lead to a significant fire hazard in an aircraft environment. The combination of the presence of an oxygen leak and standard electrical or other sources of ignition can create a dangerous scenario, resulting in a fire. This incident highlights the critical importance of proper maintenance and attention to detail in aircraft systems, particularly those involving pressurized systems such as oxygen in aircraft cabins.

Other options relate to different potential causes but do not apply to this specific incident. An electrical short circuit, for instance, could cause fires but was not the identified issue in this case. Similarly, while improper maintenance or faulty oxygen equipment could potentially contribute to other incidents, it was the specific oversight of not properly tightening the oxygen fitting that directly caused the fire in this situation.