The US Army Signal Corps K-38 trailer, cable splicer, 1/4 ton, 2 - wheel, seems to have been a standard civilian American Telephone & Telegraph designed product from the 1930s that was adopted into military service, and later augmented by the K-38A, a modified Willys MB/GPW jeep trailer which was outfitted for the same work - the repair and maintenance of lead-wiped telephone cable joints. The parts list below was published in January 1945, which supports the assumption that both types were in use at the end of World War II. Identical civilian trailers dated as late as 1948 have been found, albeit with slightly different wheels.
Although the K-38 is cited as produced by various manufacturers; the SNL-G-685 parts list reveals that the unique body parts all had AT&T part numbers.
A list of serial numbers, manufacturers and dates of delivery is in compilation, and seems to indicate that Highway Trailer made the earliest units at the start of World War II, FWD production was later in World War II, and Regent Manufacturing post World War II production.
The disc wheels, 4" wide by 18" diameter, are described as "motorcycle type". The earliest trailers had two tie-down holes stamped in a recess on either side of the wheel hub, visible in one of the images used here. Later plain wheels sometimes had a single hole cut in a corresponding place in each wheel centre, or a welded-on loop, and the post war Regent production had a different style entirely with more of a lattice section towards the outside of the centre disc. This variation can be attributed to manufacturers using whatever wheels were available at time of production, but all wheels appeared to have been made or altered to be able to be secured by hole(s) or loop.
The bracket on the top is for a fuel-burning lantern used for roadside warning purposes, and on inspection appears rather more elaborate than it needs to be. A fabricated steel guard with mesh sides was provided for the lantern. No electrical wiring was provided on the original trailer, but a single taillight and reflector were commonly added.
Security was by padlock and hasp on the main lid, the rear lower hatch being secured by a pin with a pull handle running up the rear inside of the main body.
Production quantities are not known, but serial number spread suggest that FWD alone produced something over 3000 units, and there is a known spread of at least 250 units in the Highway Trailer serial numbers.