subclass_of r23x-class airship
The British R23X class of rigid airships were developed during ___MASK1___ War I using the experiences gained from the 23 class , but only two of the planned four R23X class were built : R27 and R29 . Both were completed mid - 1918 , but just two - and - a - half months after entering ___MASK25___ R27 was destroyed by fire in a hangar ; while R29 went on to become the most successful British wartime ___MASK69___ , being the only one to meet enemy action . Genocide is intentional ___MASK51___ to destroy a ___MASK83___ ( usually defined as an ethnic , national , racial , or ___MASK81___ group ) in whole or in part . The ___MASK32___ word " genocide " is a combination of the Greek word " génos " (" race , ___MASK83___ ") and the Latin suffix "- cide " (" act of killing "). The United Nations Genocide Convention defines genocide as " acts committed with intent to destroy , in whole or in part , a national , ethnic , racial or ___MASK81___ group ". ___MASK24___ are members of the ___MASK16___ . Usually , personnel are divided into military branches roughly defined by certain circumstances of their deployment . Those who serve in a typical large land force are soldiers , making up an army . Those who serve in seagoing forces are seamen or sailors , and their branch is a navy or coast guard . Marines serve in a marine corps . In the 20th century , the development of powered ___MASK80___ ___MASK65___ prompted the development of air forces , serviced by airmen . Designated leaders of military personnel are officers . These include commissioned officers , warrant officers and non - commissioned officers ( NCOs ). For naval forces , non - commissioned officers are referred to as petty officers ( POs ). military personnel are instructed to wear dog tags Trench ___MASK47___ is a type of land ___MASK47___ using occupied fighting lines consisting largely of trenches , in which troops are significantly protected from the enemy ' s small arms fire and are substantially sheltered from artillery . The most famous use of trench ___MASK47___ is the ___MASK73___ Front in World War I . It has become a byword for stalemate , attrition , sieges and futility in conflict . A ___MASK63___ was a type of ___MASK69___ named after the German Count Ferdinand von ___MASK63___ who pioneered ___MASK69___ development at the beginning of the 20th century . ___MASK63___ ' s notions were first formulated in 1874 and developed in detail in 1893 . They were patented in Germany in 1895 and in the United States in 1899 . After the outstanding success of the ___MASK63___ design , the word " zeppelin " came to be commonly used to refer to all rigid airships . Zeppelins were first flown commercially in 1910 by Deutsche Luftschiffahrts - AG ( DELAG ), the world ' s first ___MASK37___ in revenue service . By mid - 1914 , DELAG had carried over 10 , 000 fare - paying passengers on over 1 , 500 flights . During World War I the German military made extensive use of Zeppelins as bombers and scouts , killing over 500 people in bombing raids in Britain . Because of Archimedes ' ___MASK43___ , a lifting gas is required for aerostats to create buoyancy . Its density is lower than that of air ( about 1 . 29 kg / m , 1 . 29 g / L ). Only certain lighter than air gases are suitable as lifting gases . In ___MASK72___ , a civilian is " a ___MASK57___ who is not a ___MASK2___ of the ___MASK79___ or of a police or firefighting force ", as defined by Merriam Webster ' s Dictionary . From the perspective of the U . S . ___MASK46___ of Defense , Chapter 18 of Title 10 United States Code refers to non - ___MASK79___ law enforcement officers as civilians since they are employees rather than enlisted personnel , and also in order to distinguish itself from ___MASK79___ police . In ___MASK79___ and law enforcement slang , the term " Civies " or " Civvies " are often used to refer civilian population or civilian clothing . A semi - ___MASK69___ or dirigible is an airship which has a stiff keel or truss supporting the main envelope along its length . The keel may be partially flexible or articulated and may be located inside or outside the main envelope . The outer shape of the airship is maintained by gas pressure , as with the non - rigid " blimp ". Semi - rigid dirigibles were built in significant quantity from the late 19th century but in the late 1930s they fell out of favour along with rigid airships . No more were constructed until the design was revived by the Zeppelin NT in 1997 . ___MASK1___ War I ( WWI or WW1 ), also known as the First ___MASK1___ War , or the Great War , was a global war originating in Europe that lasted from 28 July 1914 to 11 November 1918 . More than 70 million ___MASK24___ , including 60 million Europeans , were mobilised in one of the largest wars in ___MASK39___ . Over nine million combatants and seven million civilians died as a result of the war ( including the victims of a number of genocides ), a casualty rate exacerbated by the belligerents ' technological and industrial sophistication , and the tactical stalemate caused by gruelling trench warfare . It was one of the deadliest conflicts in ___MASK39___ , and paved the way for major political changes , including revolutions in many of the nations involved . A ___MASK31___ , or non - ___MASK69___ , is an airship ( dirigible ) without an internal structural framework or a keel . Unlike semi - rigid and rigid airships ( e . g . Zeppelins ), blimps rely on the pressure of the lifting gas ( usually helium , rather than hydrogen ) inside the envelope and the strength of the envelope itself to maintain its shape . The term is sometimes also used to refer to the tethered craft properly known as moored balloons . While often very similar in shape , moored balloons have no propulsion and are tethered to the ground . A ___MASK69___ is a type of airship ( or dirigible ) in which the envelope is supported by an internal framework rather than by being kept in shape by the pressure of the lifting gas within the envelope , as in blimps ( also called pressure airships ) and semi - rigid airships . Rigid airships are often commonly called Zeppelins . An ___MASK33___ or dirigible ___MASK7___ is a type of aerostat or lighter - than - air ___MASK65___ that can navigate through the air under its own power . Aerostats gain their lift from large gas bags filled with a lifting gas that is less dense than the surrounding air . In early dirigibles , the lifting gas used was hydrogen , due to its high lifting capacity and ready availability . Helium gas has almost the same lifting capacity and is not flammable , unlike hydrogen , but is rare and relatively expensive . Significant amounts were first discovered in the United States and for a while helium was only used for airships by the United States . Most airships built since the 1960s have used helium , though some have used hot air .