The designation VI103 or Valve Indicating 103, is a UK military type that predates the CV or common Valve naming system introduced in 1941.
The VI103 specification is virtually the same as the commercial Y63 in specification.
The display electrodes are symmetrical in the classic envelope.
The classic envelope is 36 mm in diameter and, excluding the IO base pins, is 87 mm tall.
References: Data-sheet, 3002, 1043 & 1040. Type VI103 was first introduced in 1937. See also 1937 adverts.