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