Many World War One aircraft used water cooled inline engines, a layout commonly seen today in four cylinder car engines. Placing the cylinders in a row, resulted in a long engine. In addition to taking up a lot of space, the long engine block and crankcase added weight. The radiator and water used for cooling also added weight. This photo shows a postwar experimental installation of an American Liberty engine in a German WW1 Fokker D7 airplane, but it nicely illustrates what an inline engine looks like. (Wikimedia Commons https://commons.wikimedia.org/wiki/File:LIberty_L-6_engine_installed_in_captured_Fokker_D.VII.jpg)