Such connections are very difficult to make at great depths of a plurality of hundreds of meters, with {HEAD ~ the difficulty} increasing at {TAIL ~ increasing depths} 
Such connections are very difficult to make at great depths of a plurality of hundreds of meters , with { HEAD ~ the difficulty } increasing at { TAIL ~ increasing depths }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL