"From other shell holes from the darkness on all sides came the groans and wails of wounded men; faint, long, sobbing moans of agony, and despairing shrieks.  It was horribly obvious that dozens of men with serious wounds must have crawled for safety into new shell holes, and now the water was rising about them, and, powerless to move, they were slowly drowning.” 

Edwin Vaughan, a British Officer, as told in John Keegan’s, "The First World War"