This type of bunker is a smallLARGE OR SMALL concrete structure, partly dug into the ground, which is usually a part of a trench system. Such bunkers give the defending soldiers better protection than the open [[trench]] and also include top protection against aerial attack. They also provide shelter against the weather. Some bunkers may have partially open tops to allow weapons to be discharged with the muzzle pointing upwards (e.g. mortars and anti-aircraft weapons).<ref name="Queen's">''[http://archives.queensu.ca/wwi/warfare.html An archival look at World War I] {{webarchive |url=https://web.archive.org/web/20081219002104/http://archives.queensu.ca/wwi/warfare.html |date=19 December 2008 }}'' from the [[Queen's University at Kingston|Queen's University]] Archives, Kingston, Ontario, Canada. Accessed 2008-02-10</ref>