The entrance-line trenches ended up backed-up by 2nd and third traces: 'assist' and 'reserve' trenches. Conversation trenches linked all of them alongside one another. This system was strengthened with fortifications, underground shelters and thick belts of barbed wire. Why the M2 Browning has stood the examination of time and study https://machguns.com/product/m10-45-acp-rpb-mac-excellent-c443/