Abstract A bank of four 3 in. gap × 12 in. wide × 7 ft long streamer chambers surrounding a one atmosphere hydrogen gas target used in an experiment to measure the threshold cross-section for the reaction π +p → π + π +n is described. Details of construction and operation are presented and photographs of representative tracks are included. This report covers research performed to September 1, 1971 including operation of the chambers during a three week run of the experiment in August 1971. A more complete set of photographs illustrating chamber response is available in J.H. Crouch and W. S. Risk, University of Maryland Technical Report No. 72-032.