The entrance-line trenches were backed-up by next and third strains: 'aid' and 'reserve' trenches. Communication trenches joined all of them alongside one another. This technique was strengthened with fortifications, underground shelters and thick belts of barbed wire. Grenades were being practical weapons for trench warfare as troops could throw them https://machguns.com/product/m10-45-acp-rpb-mac-excellent-c443/