>>64159973
>>64160060
These were my two first thoughts as well, but didn't they already try to artillery as hard as they could possibly artillery? Were there even the kinds of resources available to vastly scale barrel/shell production for any of the sides?
Tunneling is also going to be slow and dangerous, there's a whole art to counter-sapping, and if your enemy knows you're going to try, it's a lot easier for them to build defenses/listening posts and intercept your tunnels.