On 24 June 1939, the Navy awarded Aircraft Radio Corporation its first contract for the "command receiver" so well known by countless flight crews and radio amateurs after the war. This is a relatively complete set of that first production contract, for the RAT equipment. An earlier one, for the Type K set, was issued in 1937 under a "Confidential" security label (roughly today's "Secret" level) but that was for a small quantity prototype run for evaluation purposes and was never fielded as was the RAT. (See ARC Type K for photos of the receivers from that earlier set.) The contract included a similar series of RAT receivers nomenclatured RAT-1, the only difference being the operating voltage of 28 volts rather than the 14 volts required by the RAT sets. Serial numbers for those started at 1 as well. A copy of the manual is located HERE.
There are some interesting characteristics of the RAT that are not shared with the hundreds of thousands of command receivers which followed. The first is the frequency range - 13.5-20MHz and 20-27MHz. The unusually high frequency range suggests a surveillance role rather than normal Navy communications. In today's parlance, it would be known as an ELINT receiver, but there is some debate over the conclusion, as some aircraft transmitters of the 1930s like the GO-** had bands extending to 27MHz. The jury is still out. Other differences from later receivers include serial number tags for the local control boxes, black lacquered local tuning knobs, and ceramic tube sockets rather than mica filled phenolic. Also note the lack of covers for the A/B tel. switches on the front of the receiver rack. Later racks extended the threads on the switch so that a small cover could be screwed on to prevent inadvertant toggling. The tube lineup was the same as the later ARA and SCR-274N sets, which meant the 12SK7 used as the RF amplifier was being pushed a bit hard to get up to 27MHz. Production figures are hard to come by for this and the RAT-1 set, but the consensus seems to be narrowing to about 50 for each set, based on the remaining set and peripheral serial numbers. I'm keeping a list of the surviving sets, so if you have one, please send serial numbers and accessories (all ownership data is being kept confidential unless the owner permits sharing this information.)
Other views of this set can be seen below.
These receivers do not have a great deal of selectivity, requiring the preselector suspended above them to be halfway useful on the amateur bands. The preselector was made from a scrapped ZB-3/ARR-1 shell to maintain the same "look" as the rest of the WWII sets. The "dial lock" at upper right is actually a push-pull band switch from a scrapped Tektronix scope plug-in for the two bands being covered. The RATs are being used with 14 volts A+ and 28 volts B+ to ensure their preservation for posterity...the capacitors are pushing 75 years old. They work fine in this mode, though an amplifier is necessary to get enough drive for earphones or speaker. The RL-5 interphone amplifier to the right is being pressed into service for that purpose.
The dynamotors shown below are not original, as the finish on the originals is gloss black, not black wrinkle. One original has been found for this set to date, but I am still looking for another if one happens to pop up in your junk box.