This a 2500 pF (2.5 nF) 200,000 volt capacitor, as shown 75 years ago today in the August 23, 1943, issue of Broadcasting.

The part was manufactured by Federal Telephone & Radio Corp., and the magazine notes that it was constructed without strategic aluminum. The twelve plates were hollow, 3-1/3 inches thick, made of 16 gauge sheet steel welded together at the sides.

According to the magazine, the part was used in the company’s high-powered transmitter laboratories as a “phantom antenna capacitor,” which presumably means that it was part of a very large dummy load.

The same picture also appears in the May 1944 issue of Popular Science,