The ARP3 is a variable μ RF pentode. The Type designation stands for Army Receiving Pentode number three.
The 200 mA heater requirement indicates that this valve is suitable for series heater chain use, and the 13 Volt rating indicates vehicle battery operation.
Oliver Palix comments at radiomuseum.org: as with the 12Y4, the ARP3 is used in the WWII Canadian set C52.
The Marconi C52 short wave transceiver was designed for operation from a 12 Volt vehicle battery with a rotary transformer to generate the HT supply. Coverage was 1.75-16 MHz and this medium range set had an output power of 70-100 Watts CW or 45-75 Watts voice.
The envelope shows that this was made in Canada by RVC as an equivalent. The 8/43 could be the date of manufacture.
The solid screen is connected to vertical support rods and then to the cathode. An inner cylinder is the anode. The control grid is wound on copper supports.
The strap on the right connects the lower circular screen to the main screen. On the left is the wire connecting the lower screen to the cathode.
The control grid connects to the top cap and the supports do not extend downwards as far as the other grid supports.
The anode cylinder can be seen on the right within the cylindrical screen. The grid wires can just be glimpsed.
The classic envelope is 38 mm in diameter, and excluding the B7 base pins is 98 mm tall.
References: Data-sheet, 1043 & 3002. Type ARP3 was first introduced in 1934. See also1934 adverts.
