The 1613 metal pentode is designed for Class C Telephony transmitter use. It is an RF power amplifier capable of 6 Watts output at up to 45 MHz and useful output at up to 60 MHz.
The RCA logo.
The reverse shows that the 1613 is identical to the US Government VT-175.
The thin metal tube envelope is 24 mm in diameter, and excluding the IO base pins is 67 mm tall.
References: Data-sheet & 4038. Type 1613 was first introduced in 1943. See also1943 adverts.