Original sentence: On several occasions, German tunnelers were within metres of large British mine "chambers".Over a period beginning more than a year before the attack, Canadian, Australian, and British engineers tunneled under the German trenches and laid 21 mines totaling 455 tonnes of ammonal explosive
Edited sentence: On several occasions, German tunnellers were within metres of large British mine "chambers".Over a period beginning more than a year before the attack, Canadian, Australian, and British engineers tunnelled under the German trenches and laid 21 mines totaling 455 tonnes of ammonal explosive