After the first tunnel, use a carried item to knock down the ladder then climb up and dig out the item from the dirt on the left side (dig up the bone ahead if you need a carried item).
"The majority of soldiers believed in God and some wore symbols of their religion. War officers had to make provisions for different religions and a variety of religious ceremonies was performed at the front by different faiths. Priests, vicars and rabbis offered succour and compassion to soldiers. Muslim soldiers from colonies were organised into separate battalions for practical reasons and their beliefs were also respected: Halal food was provided as well as Muslim Funeral services."