forced march vs yomp

forced march

noun
  • A movement on foot by soldiers or prisoners of war, who must, in order to satisfy a military requirement, travel at a speed or in adverse conditions that would normally tire them excessively. 

yomp

noun
  • A long-distance march carrying full kit. 

verb
  • To make a strenuous long-distance march. 

How often have the words forced march and yomp occurred in a corpus of books? (source: Google Ngram Viewer )