The 913 is a 1936 one inch CRT in a metal envelope. When released by RCA the price was considerably lower than the same sized CRTs then available.
The tube produces a green trace with a medium persistence phosphor. The final anode and one side of the deflection plates are brought out to a single pin and thus the deflection is for single ended amplifiers only.
RCA introduced the Model 151 general purpose oscilloscope in late 1936 and used the 913 as the tube.
The International Base and RCA logo.
The top of the envelope with the one inch domed window.
The viewing window.
The wide metal tube envelope is 32 mm in diameter and, excluding the IO base pins, is 94 mm tall.
References: Datasheet, & www.edn.com. Type 913 was first introduced in 1936.