187153
Many of them were " Bantams " , soldiers of below average height who had been rejected from regular units because they did not meet the height requirements ; others had been initially rejected as too old , but their specialist mining experience made them essential for the tunnelling operation .
 tunnelling
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 tunnelling