KC-130: What are the four tanks/tube on the wings in between the engines used for?
The tanks between the engines on each wing are external fuel tanks. The pods outboard of the #1 and #4 engines are aerial refueling pods which house the hoses and drogues that are reeled out when refueling other aircraft.

This page has several examples of the outboard pods trailing drogues for refueling.  These pods are unique to KC- and MC-130 variants. One example:



The inboard external tanks (between engines 1 &amp; 2 and 3 &amp; 4) are found on most variants of the C-130.