Production of GP-4u started in 1955 and ended in 1974. The face piece name is M49 and is issued with a "Coffee Can" type filter and is designated GP-4u, it comes in either gray or brown; the common colour for coffee can type filters. Where the inlet valve is found is an irremovable hose kept in place by a darker gray band. The exhale valve is in a metal assembly, similar to the pdf-d but with a slight tint of tan. Because of the mask's simplistic design, it does toll the wearer by fogging up very easily as it has only a very simple inlet and exhale valve. Like other Cold War Era GP series masks, it comes with a green haversack with several pockets and one button.