Describe the technique, called the "cut-and-cover", that was used in the late 1800's

cut and cover is a simple method of construction for shallow tunnels where a trench is excavated and roofed over with an overhead support system strong enough to carry the load of what is to be built above the tunnel. ... Excavation then takes place under the permanent tunnel roof, and the base slab is constructed.

Explanation:

c) troops march forward in close formation against newer, more accurate weapons

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