The airplane is a C-130 Hercules and the door on the side of the fuselage is used very rarely. Most likely the crew chief and/or loadmaster were simply looking or taking photos. This is one of the few airplanes to be in service for more than 50 years with the original customer - US Air Force. I have a lot of hours on these and this would seem to be the RAF version with the extended fuel tanks and no markings that I can discern.

Captain One Iron