It is clear that by civil standards the aircraft are under used, perhaps you should start to ask why when deployed on tactical tasks you only have one crew. It would seem to me that a valuble asset is sitting on the ground waiting for the crew to rest, brief and plan when if more crews are made avalable the aircraft could be working.
Aircraft requires refuelling, servicing, minor (and sometimes major) rectification, re-arming and re-roling.
While the crew is 'resting' all this is carried out by only a few engineers who also have maybe 3 or 4 other frames to look after.
Unfortunately we don't have the luxury of pitching up an hour before to a fully prepped aircraft, with all our planning done by a despatch system, with only a black leather flight bag, to monitor the autopilot for 10 hours before relaxing in a hotel for 3 days.
One crew, one airframe works well for tactical ops as a lot of the time the crew have to live in the back of the aircraft!
5 airframes would allow 4 to be used, with an in-theatre spare, or to allow one to be in deep servicing.
We have a better crew to airframe ratio for strategic ops - believe me our AT fleet is not sat around idle.
5 more C130Js would certainly help with both hub and spoke strat lift and relieve the pressure on the in-theatre tac airlift fleet.